Treatment of cancer with imidazo-1,2-pyridazin compounds

ABSTRACT

Compounds of general formula (I) ##STR1## wherein R 1  represents an optionally substituted carbocyclic or heterocyclic aryl group, or an optionally substituted alkyl, alkenyl, cycloalkyl or cycloalkenyl group; R 2  represents an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group or an optionally substituted carbocyclic or heterocyclic aryl or aralkyl group; R 3  represents a hydrogen atom or an alkyl group; and either X represents an oxygen or sulphur atom, a group, --CH 2  -- or a group NR 4  where R 4  represents a hydrogen atom or a C 1-4  alkyl group; and Y represents a group --CH 2  -- or --CH 2  CH 2  -- or X--Y together represent the group --CH═CH--; and salts and physiologically functional derivatives thereof are useful in the treatment of tumors. Processes for preparing the compounds, intermediates useful in their preparation, pharmaceutical compositions containing them and their use in the treatment of tumors are also described.

This is a continuation of application Ser. No. 08/272,326 filed on Jul. 8, 1994, now abandoned, which is a division of Ser. No. 08/123,529, filed Sep. 17, 1993, now U.S. Pat. No. 5,380,759, which is a division of Ser. No. 07/817,539, filed Jan. 7, 1992, now abandoned, which is a continuation of Ser. No. 07/231,894, filed Aug. 12, 1988, now U.S. Pat. No. 5,091,531.

The present invention relates to heterocyclic compounds which have been found to have cytotoxic activity. More specifically, the invention concerns imidazopyridazine derivatives, methods for their preparation, pharmaceutical formulations containing them and their use as cytotoxic agents, in particular as antitumour agents.

Research in the area of cancer chemotherapy has produced a variety of antitumour agents, which have differing degrees of efficacy. Standard clinically used agents include adriamycin, actinomycin D, methotrexate, 5-fluorouracil, cis-platinum, vincristine and vinblastine. However, these presently available anti-tumour agents are known to have various disadvantages, such as toxicity to healthy cells and resistance to certain tumour types.

In addition to having anti-tumour activity, vincristine is know to be an inhibitor of microtubule function. Other compounds which exhibit microtubule inhibitory activity and which have been reported to be potential antitumour agents are nocodazole, tubulazole and NSC - 181928; ##STR2## However, none of these compounds has yet been proven clinically.

There is thus a continuing need for new and improved anti-tumour agents.

We have now found a novel class of imidazopyridazine derivatives which exhibit potent anti-tumour activity.

In a first aspect, the present invention provides a compound of general formula (I) ##STR3## wherein R¹ represents an optionally substituted carbocyclic or heterocyclic aryl group, or an optionally substituted alkyl, alkenyl, cycloalkyl or cycloalkenyl group;

R² represents an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group or an optionally substituted carbocyclic or heterocyclic aryl or aralkyl group;

R³ represents a hydrogen or an alkyl group;

and either

X represents an oxygen or sulphur atom, a group --CH₂ -- or a group NR⁴ where R⁴ represents a hydrogen atom or a C₁₋₄ alkyl group; and

Y represents a group --CH₂ -- or --CH₂ CH₂ --

or

X--Y together represent the group

    --CH═CH--;

and salts and physiologically functional derivatives thereof.

Referring to the groups R¹ and R² in the general formula (I) a carbocylic aryl group may contain 6 to 10 ring members, e.g. phenyl and naphthyl, and contains at least one aromatic ring. A heterocyclic aryl group may contain from 5-10 atoms in the ring, at least one of which is a heteroatom. The heterocyclic ring typically contains from 1-4 heteroatoms selected from nitrogen, oxygen and sulphur. Examples of suitable heterocyclic rings include thienyl, furyl, pyridyl, indole and quinoline rings.

Substituents which may be present on the carbocyclic or heterocyclic aryl group include C₁₋₆ alkyl, C₁₋₄ alkoxy (which may itself be optionally substituted by a C₁₋₂ alkoxy or C₁₋₂ alkoxy-C₁₋₂ alkoxy group), halogen (e.g. fluorine, chlorine or bromine), amino (optionally substituted by one or two C₁₋₄ -alkyl group), C₁₋₄ haloalkyl (e.g. trifluoromethyl), C₁₋₄ alkylthio, carboxy, C₁₋₄ alkoxycarbonyl, --SO₃ H, cyano and phenyl. The carbocylic or heterocyclic aryl group may suitably carry from 1 to 4 substituents.

Unless otherwise indicated, alkyl groups R¹ and R² present in general formula (I) may be straight or branched chain alkyl groups, and may contain 1-10 carbon atoms, e.g. 3-10 carbon atoms. An alkenyl or alkynyl group may contain 2-10 carbon atoms e.g. 3-10 carbon atoms. A cycloalkyl or cycloalkenyl group may contain from 3-10 carbon atoms. Substituents which may be present on an alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group include halogen atoms, C₁₋₄ alkoxy groups, hydroxy, amino (optionally substituted by one or two C₁₋₄ alkyl groups) C₁₋₄ haloalkyl (e.g. trifluoromethyl), C₁₋₄ alkylthio, carboxy, C₁₋₄ alkoxycarbonyl, --SO₃ H and cyano.

When R² represents an aralkyl group this may contain from 1 to 4 atoms in the alkyl portion and the aryl portion may be a carbocylic or heterocyclic aryl group as defined above for R¹ and R².

When R¹ represents an alkyl group this preferably contains more than two carbon atoms, e.g. C₃₋₆ alkyl.

When R² represents an alkyl group this preferably contains from 1 to 6 carbon atoms, 1 to 4 carbon atoms.

When R³ or R⁴ represents an alkyl group this may be straight or branched chain and may contain 1-4 carbon atoms.

Certain compounds of formula (I) may form salts. Thus, compounds (I) which contain a basic amino group may form salts with acids, and compounds which contain an acidic group may form salts with bases.

Suitable acid addition salts include those formed from hydrochloric, hydrobromide, nitric, perchloric, sulphuric, citric, tartaric, phosphoric, lactic, benzoic, glutamic, oxalic, aspartic, pyruvic, acetic, succinic, fumaric, maleic, oxaloacetic, isothionic, stearic, phthalic, methanesulphonic, p-toluene sulphonic, benzenesulphonic, lactobionic and glucuronic acids. Suitable base salts include inorganic base salts such as alkali metal (e.g. sodium and potassium) salts and alkaline earth metal (e.g. calcium) salts; organic base salts e.g. phenylethylbenzylamime, dibenzylethylenediamine, ethanolamine and diethanolamine salts; and amino acid salts e.g. lysine and arginine. Most preferably, the salts will be pharmaceutically acceptable.

In the compounds of general formula (I) R¹ preferably represents an optionally substituted phenyl or naphthyl group, an optionally substituted 5-or 6-membered heterocyclic aryl group, containing from 1 to 4, e.g. 1 or 2, heteroatoms selected from nitrogen, oxygen and sulphur. Preferred substituents which may be present in the group R¹ include C₁₋₄ alkoxy, C₁₋₄ alkyl, and mono-or-di-(C₁₋₄)alkylamino groups and halogen atoms. R¹ further preferably represents an unsubstituted alkyl group, e.g. a C₃₋₆ alkyl group.

R² preferably represents a phenyl group or an optionally substituted C₁₋₄ alkyl group. Preferred substituents which may be present in the group R² include C₁₋₁₄ haloalkyl (e.g. trifluoromethyl), C₁₋₄ alkoxy, hydroxy, halogen, mono-or-di-(C₁₋₄)alkylamino and nitrogen-attached 5-or-6 membered heterocyclic groups (e.g. morpholine, piperidino, pyrrolidino). Advantageously R² is a C₁₋₄ -alkyl group.

R³ is preferably hydrogen or methyl.

Y preferably represents --CH₂ --. The group --Y--X-- preferably represents --CH₂ O--, --CH₂ S--, --CH₂ CH₂ -- or --CH═CH--

A particularly preferred group of compounds of formula (I) are those in which

R¹ represents a phenyl or naphthyl group which may be substituted by 1 to 4 substituents selected from C₁₋₄ -alkoxy (eg methoxy or ethoxy), C₁₋₄ alkyl (eg methyl, ethyl, n-propyl, i-propyl, n-butyl or t-butyl), and halogen (eg bromine or chlorine);

R² represents a C₁₋₄ alkyl group (preferably methyl or ethyl);

R³ represents hydrogen or methyl; and

Y--X represents the group --CH₂ O--;

and salts and physiologically functional derivatives thereof.

Particularly preferred compounds according to the present invention on the basis of their activity, include:

methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(3,5-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(2,5-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(1-naphthylmethyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(3-methylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(2,3-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(2,5-dimethylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

ethyl N-[6-(2,5-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

ethyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-methyl-N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(2-bromo-3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

n-propyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, and

n-butyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

2-methoxyethyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

methyl N-[6-(3,5-dimethoxy-4-ethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate,

and physiologically functional derivatives thereof.

Compounds of the present invention have cytotoxic activity, i.e. they are toxic to certain living cells which are detrimental to mammals, for example tumour cells.

The antitumour activity of compounds of general formula (I) has been demonstrated in a number of standard tests both in vitro and in vivo, primarily by activity against murine leukaemic cell lines e.g. P388.

Thus, compounds of general formula (I) have been found to exhibit potent anti-tumour activity against P388 in vitro in proliferative assays and in the more stringent colony-forming assays. In vivo, compounds of the invention effected a reduction in the number of tumour cells in mice bearing ascitic P388/0 leukaemia tumours, and a consequent increase in survival duration as compared to an untreated tumour bearing control group.

Activity in the above standard in vivo tumour test has been reported to be indicative of antitumour activity in man (A. Goldin et al, in Methods in Cancer Research, ed. V. T. DeVita Jr. and H. Busch, 16 198-199, Academic Press N.Y.-1979).

Compounds of the invention have also been found to interfere with tubulin function, as evidenced by inhibition of tubulin polymerisation in vitro.

It has previously been reported that compounds which act as microtubule inhibitors appear to block the directional migration of tumour cells. It is therefore believed that compounds of the present invention will have anti-invasive and antimetastatic properties.

In addition to the above described properties, several preferred compounds of the invention have been found to exhibit activity against a variety of human tumour cell lines in vitro (DLD-1 human colon carcinoma, WiDr human colon adenocarcinoma, HCT-116 human colon carcinoma and A549 human lung carcinoma) indicating that the compounds have broad spectrum antitumour activity.

A particularly preferred compound on the basis of its activity is methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, and physiologically functional derivatives thereof. This compound has further been found to exhibit good activity against various murine tumours in vivo (B16 melanoma and L1210 leukaemia). In addition it has also been found advantageously to exhibit good activity in vivo against strains of P388 which are resistant to the major clinically used anti-tumour agents including cyclophosphamide, methotrexate, actinomycin D, vincristine, adriamycin, 5-fluorouracil, cis-platinum, bis-chloronitrosourea and amsacrine. It is believed that the adriamycin, vincristine and actinomycin D-resistant tumours are in fact resistant to a wide variety of antitumour drugs.

Without wishing to be bound by theory it is believed that certain compounds according to the invention act as pro-drugs. Thus, compounds of formula (I) wherein R³ is an alkyl group have higher activity in vivo than would be expected on the basis of their in vitro activity, and it is believed that they are converted in vivo into a compound of formula (I) wherein R¹ is hydrogen.

According to a further aspect, the present invention also provides a process for preparing compounds of general formula (I), which process comprises:

(A) reaction of a pyridazine derivative of general formula (II) ##STR4## (wherein R¹, and X and Y are as hereinbefore defined) with a compound of general formula (III): ##STR5## (wherein R² and R³ are as hereinbefore defined and Z represents a halogen atom e.g. a chlorine or bromine atom).

(B) reaction of a pyridazine derivative of general formula (IV) ##STR6## (wherein R² and R³ are as hereinbefore defined and Z¹ represents a leaving group such as a halogen atom or sulphonate group, e.g. methane sulphonate or p-toluene sulphonate) with a compound of general formula (V)

    R.sup.1 CH.sub.2 X.sup.1 H                                 (V)

(wherein R¹ is as hereinbefore defined and X¹ represents an oxygen or sulphur atom or a group NR⁴ as hereinbefore defined);

(C) reaction of a compound of formula (VI) ##STR7## with an appropriate alcohol R² OH

(D) reaction of a compound of formula (VII) ##STR8## with a reagent serving to introduce the group --CO₂ R²

(E) conversion of one compound of formula (I) into another compound of formula (I) for example by exchanging one esterifying group R² for a different esterifying group R² ; or by alkylation of a compound of formula (I) wherein R³ represents hydrogen; followed if desired and/or appropriate by salt formation.

General process (A) may conveniently be effected in an aprotic solvent, such as dimethylformamide, 1,3-dimethylimidazolidinone, or hexamethylphosphoramide, and at a non-extreme temperature, for example at between 50°-120° C.

Compounds of general formula (II) wherein X represents an oxygen or sulphur atom or a group NR⁴ may be prepared by reaction of an appropriate alcohol, thiol or amine of formula (V) as defined above with a compound of formula (VIII): ##STR9## (wherein Z¹ is as hereinbefore defined).

The reaction will generally be conducted in the presence of a base, such as potassium t-butoxide in a solvent such as dimethoxyethane. Alternative bases and solvents which may be employed in this reaction include sodium hydride in an aprotic solvent such as dimethylformamide or dimethyl sulphoxide, and sodium methoxide or ethoxide in an alcohol such as methanol or ethanol, or an aprotic solvent such as those mentioned hereinabove.

Compounds of formula (II) wherein X and Y together represent the group --CH═CH-- may be prepared from a compound of formula (IX) by successive reactions with a halogenating agent such as phosphorous trichloride and ammonia. ##STR10##

Compounds of formula (IX) may be prepared by reacting an appropriate arylaldehyde R¹ CHO with 3-oxopentanoic acid (laevulinic acid) in the presence of a base in aqueous alcohol followed by reaction with hydrazine under acidic conditions to give a compound of formula (X): ##STR11## which may be dehydrogenated e.g. using selenium dioxide in an alcohol e.g. ethanol to give a compound of formula (IX).

When it is desired to prepare compounds of formula (II) wherein X and Y are both methylene groups the ethenyl moiety in the compound of formula (IX) or (X) may first be reduced, for example by catalytic hydrogenation using e.g. palladium on charcoal.

Compounds of formula (III) may be prepared by reaction of the corresponding haloacetamide of formula (XI): ##STR12## with oxalyl chloride, and an alcohol R² OH, according to methods well known in the art.

Alcohols of general formula (V) may be prepared from the corresponding carboxylic acids or carboxaldehydes using standard procedures, e.g. by reduction with sodium borohydride in a solvent such as methanol or ethanol, or with lithium aluminium hydride in a solvent such as diethyl ether or tetrahydrofuran.

A thiol of general formula (V) may be prepared from the corresponding halide R¹ CH₂ Z³ (wherein Z³ is a halogen atom) be reaction with thiourea in a solvent such as ethanol, to give the corresponding isothiouronium salt, and subsequent hydrolysis e.g. with sodium hydroxide solution.

Amines of general formula (V) may be prepared in conventional manner, by reaction of a corresponding halide with ammonia.

Reaction of a compound of general formula (IV) with a compound of general formula (V) according to process (B) will generally be effected in the presence of a base. Suitable bases include alkali metal alkoxides such as sodium or potassium methoxide, ethoxide or t-butoxide. The reaction may be conveniently carried out in a solvent, such as dimethoxyethane; an alcohol e.g. methanol or ethanol, or an aprotic solvent such as dimethylformamide or dimethylsulphoxide.

Compounds of general formula (IV) may be prepared by reacting a compound of formula (VII) with a compound of formula (III) in an analogous manner to general process (A) described above.

General process (C) may be effected by heating a compound of formula (VI) to a temperature in the range 80° to 120° C., optionally in the presence of a solvent, and reacting with an alcohol R² OH.

Suitable solvents include inert organic solvents such as hydrocarbons e.g. benzene or toluene. Alternatively the alcohol R² OH may itself act as the solvent.

It is believed that process (C) proceeds via an intermediate isocyanate derivative of formula (XII) ##STR13## Acyl-azide derivatives of formula (VI) may be prepared from the corresponding carboxylic acids by formation of an activated acid derivative, (e.g. an acid halide such as an acid chloride formed by reaction with a halogenating agent such as oxalyl chloride, thionyl chloride or phosphorus pentachloride) followed by reaction with an azide e.g. an alkali metal azide, conveniently in an aqueous ether solution e.g. aqueous dioxan. The carboxylic acid derivatives corresponding to compounds (VI) may themselves be prepared by reacting a compound of formula (II) with ethyl bromopyruvate using analogous conditions to general process (A) above, to give an ester, followed by hydrolysis to give the desired acid.

In process (D) a reagent serving to introduced the group --CO₂ R² may be the corresponding haloformate, e.g. an alkylhaloformate such as methyl-or ethyl-chloroformate. Compounds of formula (VII) may themselves be prepared from a compound of formula (I) by removal of a group --CO₂ R², (preferably a labile group such as t-butoxycarbonyl) under acid conditions (using e.g. an optionally halogenated carboxylic acid such as formic, chloroformic or trifluoacetic acid), optionally in the presence of a solvent, e.g. a halogenated hydrocarbon such as dichloromethane. Thus, in a particular embodiment of process (D) one compound of formula (I) may be converted into a different compound of formula (I), by removal of one group --CO₂ R² and reaction to introduce a different group --CO₂ R² as described above.

Conversion of a compound of formula (I) into a different compound of formula (I) according to general process (E) may be achieved for example by replacing an esterifying group R² in the compound of formula (I) by a different group R² by heating a compound (I) with an appropriate alcohol in the presence of a base, for example an alkali metal alkoxide such as potassium t-butoxide, at a temperature in the range 50° to 180° C. Whilst such ester exchange may be carried out as a separate reaction step, it may also conveniently be effected during the course of the reaction between a compound of formula (IV) with a compound (V) according to general process (B).

Interconversion according to process (E) may also be achieved by alkylation of a compound wherein R³ is a hydrogen atom, to provide a compound wherein R³ is an alkyl group. Alkylation may be effected in conventional manner, for example, using an alkyl halide, e.g. methyl or ethyl iodide, in the presence of a base, e.g. sodium hydride.

Those intermediates of formulae (II) to (XI) which are novel form a further aspect of the present invention. Preferred intermediates are those of formulae (II), (IV) and (VI).

The compounds of the present invention are useful for the treatment of tumours. They may be employed in treating various forms of cancer including leukaemias, lymphomas, sarcomas and solid tumours.

The invention thus further provides a method for the treatment of tumours in animals, including mammals, especially humans, which comprises the administration of a clinically useful amount of compound of formula (I) or a pharmaceutically acceptable salt or physiologically functional derivative in a pharmaceutically useful form, once or several times a day or in any other appropriate schedule, orally, rectally, parenterally, or applied topically.

In addition, there is provided as a further, or alternative, aspect of the invention, a compound of formula (I) or a pharmaceutically acceptable salt or physiologically functional derivative thereof for use in therapy, for example as an antitumour agent.

The amount of compound of formula (I) required to be effective as a cytotoxic agent will, of course, vary and is ultimately at the discretion of the medical or veterinary practitioner. The factors to be considered include the condition being treated, the route of administration, and nature of the formulation, the mammal's body weight, surface area, age and general condition, and the particular compound to be administered. A suitable effective antitumour dose is in the range of about 0.01 to about 120 mg/kg body weight, e.g. 0.1 to about 120 mg/kg body weight, preferably in the range of about 0.1 to 50 mg/kg, for example 0.5 to 5 mg/kg. The total daily dose may be given as a single dose, multiple doses, e.g., two to six times per day or by intravenous infusion for selected duration. For example, for a 75 kg mammal, the dose range would be about 8 to 9000 mg per day, and a typical dose could be about 50 mg per day. If discrete multiple doses are indicated treatment might typically be 15 mg of a compound of formula (I) given up to 4 time per day.

Whilst it is possible for the active compound to be administered alone, it is preferable to present the active compound in a pharmaceutical formulation. Formulations of the present invention, for medical use, comprises a compound of formula (I) or a salt thereof together with one or more pharmaceutically acceptable carriers and optionally other therapeutic ingredients. The carrier(s) should be pharmaceutically acceptable in the sense of being compatible with the other ingredients of the formulation and not deleterious to the recipient thereof.

The present invention, therefore, further provides a pharmaceutical formulation comprising a compound of formula (I) or a pharmaceutically acceptable salt or physiologically functional derivative thereof together with a pharmaceutically acceptable carrier therefor.

There is also provided a method for the preparation of a pharmaceutical formulation comprising bringing into association a compound of formula (I) or a pharmaceutically acceptable salt or physiologically functional derivatives thereof, and a pharmaceutically acceptable carrier therefor.

Formulations according to the present invention include those suitable for oral, topical, rectal or parenteral (including subcutaneous, intramuscular and intravenous) administration. Preferred formulations are those suitable for oral or parenteral administration.

The formulations may conveniently be present in unit dosage form and may be prepared by any of the methods well known in the art of pharmacy. All methods include the step of bringing the active compound into association with a carrier which constitutes one or more accessory ingredients. In general, the formulations are prepared by uniformly and intimately bringing the active compound into association with a liquid carrier or a finely divided solid carrier or both and then, if necessary, shaping the product into desired formulations.

Formulations of the present invention suitable for oral administration may be presented as discrete units such as capsules, cachets, tablets or lozenges, each containing a predetermined amount of the active compound; as a powder or granules; or a solution or suspension in an aqueous or non-aqueous liquid such as a syrup, an elixir, an emulsion or a draught.

A tablet may be made by compression or moulding, optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine the active compound in a free-flowing form such as a powder or granules, optionally mixed with a binder, lubricant, inert diluent, surface active or dispersing agent. Moulded tablets may be made by moulding in a suitable machine a mixture of the powdered active compound with any suitable carrier.

A syrup may be made by adding the active compound to a concentrated, aqueous solution of a sugar, for example sucrose, to which may also be added any accessory ingredients. Such accessory ingredient(s) may include flavourings, an agent to retard crystallization of the sugar or an agent to increase the solubility of any other ingredients, such as a polyhydric alcohol for example glycerol or sorbitol.

Formulations for rectal administration may be presented as a suppository with a conventional carrier such as cocoa buffer.

Formulations suitable for parenteral administration conveniently comprise a sterile aqueous preparation of the active compound which is preferably isotonic with the blood of the recipient. Such formulations suitably comprise a solution of a pharmaceutically and pharmacologically acceptable acid addition salt of a compound of the formula (I) that is isotonic with the blood of the recipient.

Useful formulations also comprise concentrated solutions or solids containing the compound of formula (I) which upon dilution with an appropriate solvent give a solution for parenteral administration as above.

In addition to the aforementioned ingredients, the formulations of this invention further include one or more accessory ingredient(s) selected from diluents, buffers, flavouring agents, binders, surface active agents, thickeners, lubricants, preservatives (including antioxidants) and the like.

In a further aspect the present invention provides the use of a compound of formula (I) or a pharmaceutically acceptable salt or physiologically functional derivative thereof for the manufacture of a medicament for the treatment of tumours.

The invention will now be illustrated by the following non-limiting Examples.

All temperatures are in degrees Celsius (°C.).

Proton nuclear magnetic resonance spectra were obtained on a Bruker AH200 FT NMR or a Bruker HFX90 FT NMR machine.

The following abbreviations are used in the preparations and Example

DME--dimethoxyethane

DMEU--1,3-dimethyl-2-imidazolidone.

LAH--lithium aluminumum hydride.

PREPARATION OF INTERMEDIATES INTERMEDIATE 1 3-Amino-6-(3,4,5-trimethoxybenzyloxy)pyridazine

3,4,5-Trimethoxybenzyl alcohol (Aldrich 19.82 g, 0.1 mol), dissolved in DME (20 ml), was added over 15 mins to a suspension of potassium t-butoxide (11.22 g, 0.1 mol) in DME (80 ml) with stirring under N₂ and cooling in an ice-bath. After 0.5 h the mixture was treated with 3-amino-6-chloropyridazine (Helv. Chim. Acta. 1954, 37, 121, J. Druey. Kd.Meier and K. Eichenberger) (12.95 g, 0.1 mol) and after 1.5 h was heated under reflux for 3 h. The mixture was cooled and filtered and the filtered solid washed with ether. The filtrate was evaporated in vacuo to give an oil which was partitioned between ethyl acetate and water. The organic phase was washed with water, dried (Na₂ SO₄) and evaporated to give an oil (A) which was chromatographed on silica gel eluting with 5% methanol-chloroform. Eluted fractions were combined to give an oil (B) which was triturated with chloroform and di-isopropyl ether to yield the title compound as an off-white solid (9.44 g), m.p.=142°-4°; Nmr. δH (CDCl₃) 6.87 (1 H, J_(AB) 8.8 Hz 5-H), 6.78 (1 H, J_(AB) 8.8 Hz, 4-H), 6.72 (2 H, s, PhH), 5.38 (2 H, s, CH₂), 4.45 (2 H, br, s, NH₂) 3.87 (6 H, s, OMe) and 3.84 (3 H, s, OMe).

INTERMEDIATE 2 3-Amino-6-(2,5-dimethoxybenzyloxy)pyridazine

2,5-Dimethoxybenzyl alcohol (30.6 g, 0.182 mol) in DME (20 ml) was added to potassium t-butoxide (20.38 g, 0.182 mol) in DME (60 ml) with stirring under N₂ and cooling in an ice-bath. After 0.5 h, the mixture was treated with 3-amino-6-chloropyridazine and after 1.5 hours was heated under reflux for 5 h, then cooled and filtered. The filtrate was evaporated in vacuo and partitioned between ethyl acetate and water. The organic phase was washed with water, dried (Na₂ SO₄) and evaporated to give a solid (A) which was recrystallised from toluene to give a solid (B). This was chromatographed on silica gel eluting with 5% methanol-chloroform to yield the title compound as a white solid (27 g), m.p.=94°-94.5°, Nmr δ_(H) (CDCl₃) 7.05 (1 H, m, PhH), 6.90-6.73 (4 H, m, ArH), 5.42 (2 H, s, CH₂), 4.5 (2 H, brs, NH₂) and, 3.78 and 3.75 (6H, s, OMe).

INTERMEDIATES 3 TO 12

The following compounds were prepared from the appropriate alcohol by the general procedure described for Intermediates 1 and 2:

(3) 3-Amino-6-(1-naphthylmethyloxy)pyridazine, m.p. 143°-144°, Nmr δ_(H) (d₆ -DMSO) 8.00 (3H, m, napth H), 7.55 (4H, m, napth H), 6.97 (1 H, J_(AB) 8.8 Hz 4-H), 6.89 (1 H, J_(AB) 8.8 Hz 5-H), 6.0 (2 H, s, CH₂) and 5.80 (2 H, s, NH₂). (From 1-naphthylmethanol, Aldrich)

(4) 3-Amino-6-(3-methoxybenzyloxy)pyridazine, m.p. 55°-60°, Nmr δ_(H) (d₆ -DMSO) 7.38 (1 H, dd, J8-4Hz, PhH), 7.13-6.89 (5 H, m, ArH), 6.05 (2 H, s, NH₂), 5.35 (2 H, s, CH₂) and 3.82 (3 H, s, OMe).

(5) 3-Amino-6-(3,5-dimethoxybenzyloxy)pyridazine, m.p. 89°-92°, Nmr δ_(H) (d₆ -DMSO) 6.88 (1 H, J_(AB) 8.8 Hz, 5-H), 6.75 (1 H, J_(AB) 8.8 Hz, 4-H), 6.62 (2 H, d, 2'-H and 6'-H), 6.42 (1 H, t, 4'-H), 5.35 (2H, s, CH₂), 4.53 (2 H, br, s, NH₂) and 3.75 (6 H, s, OMe).

(6) 3-Amino-6-(3-Methylbenzyloxy)pyridazine, Nmr δ_(H) (d₆ -DMSO) 7.40-7.10 (4H, m, PhH), 6.90 (2 H, J_(AB) 8.8 Hz, 4-H and 5-H), 5.91 (2 H, br, s, NH₂), 5.17 (2 H, s, CH₂) and 2.31 (3 H, s, Me); M/Z 215 (M⁺, 30%), 198 (9), 123 (23), 111(31) and 105(100).

(7) 3-Amino-6-(3-dimethylaminobenzyloxy)pyridazine, m.p. 127°-129°, Nmr δ_(H) (d₆ -DMSO) 7.25 (1 H, t, 5'-H), 7.00 (1 H, J_(AB) 8.8 Hz, 4-H), 6.92 (1 H, J_(AB) 8.8 Hz, 5-H), 6.90-6.70 (3H, m, 2'-, 4'- and 6'-H), 5.95 (2 H, s, CH₂), 5.30 (2 H, br.s,NH₂) and 2.98 (6H, s, NMe₂). (From 3-dimethylaminobenzylalcohol, prepared by LAH reduction of 3-dimethylaminobenzoic acid, Aldrich)

(8) 3-Amino-6-(2-methoxybenzyloxy)(pyridazine, m.p. 166°-168°, Nmr δ_(H) (CDCl₃) 7.8 (1 H, dd, J6.7 and 2.2 Hz, PhH), 7.30 (1 H, dd, J6.6 and 2.2 Hz, PhH), 6.98 (1 H, dt, J6.6 Hz, PhH), 6.92 (1 H, d, J6.6 Hz, PhH), 6.90 (1 H, J_(AB) 8.8 Hz, 5-H), 6.78 (1 H, J_(AB) 8.8 Hz, 4-H), 5.5 (2 H, s, CH₂), 4.42 (2 H, br.s, NH₂) and 3.87 (3H, s, OMe).

(9) 3-Amino-6-[3,5-dimethoxy(4-methoxyethoxymethoxy)benzyloxy]pyridazine, m.p. 110°-114°, Nmr, δ_(H) (CDCl₃) 6.88 (1 H, J_(AB) 8.8 Hz, 5-H), 6.78 (1 H), J_(AB) 8.8 Hz, 4-H), 6.7 (2H, 5,2'- and 6'-H), 5.35 (2 H, s, CH₂), 5.2 (2 H, s, CH₂), 4.49 (2 H, br.s, NH₂), 4.05 (2 H, m, CH₂) 3.85 (6 H, s, OMe), 3.61-3.51 (2 H, m, CH₂) and 3.35 (3 H, s, OMe).

(10) 3-Amino-6-(3-chlorobenzyloxy)pyridazine, Nmr δ_(H) (d₆ -DMSO) 7.51-7.32 (4 H, m, PhH), 6.91 (2 H, J_(AB) 8.8 Hz, 4 H and 5-H), 5.92 (2 H, br.s, NH₂) and 5.34 (2 H, s, CH₂); M/Z 235 (M⁺, 68%), 218(10), 125 (65) and 97 (100).

(11) 3-Amino-6-(2-thienylmethyloxy)pyridazine, m.p. 101°-103°, Nmr δ_(H) (d₆ -DMSO), 7.52 (1 H, d, 5'-H), 7.20 (1 H, d, 3'-H), 7.02 (1 H, dd, 4'-H), 6.94 and 6.85 (2 H, J_(AB) 8.8 Hz, 4-H and 5-H), 5.95 (2 H, s, CH₂) and 5.50 (2 H, s, NH₂).

(12) 3-Amino-6-(3,4,5-trimethoxybenzylthio)pyridazine was prepared according to the method described for Intermediates 1 and 2 using 3,4,5-trimethoxybenzylthiol and 3-amino-6-chloro pyridazine to give the product, m.p. 143°-146°, Nmr δ_(H) (CDCl₃) 7.07 and 6.63 (2 H, J_(AB) 8.8 Hz, 4-H and 5-H), 6.66 (2 H, s, PhH) 4.63 (2 H, br.s, NH₂), 4.44 (2 H, s, CH₂), 3.85 (6 H, s, OMe) and 3.84 (3 H, s, OMe).

INTERMEDIATE 13 2-Methoxyethyl N-chloroacetylcarbamate

The procedure described by R. J. Bochis et al. J.Med.Chem 1978, 21, 235 were followed to yield the title compound m.p. 97°-99°, Nmr δ_(H) (d₆ -DMSO) 11.07 (1 H, br.s, NH), 4.56 (2 h, s, ClCH₂), 4.28 (2 H, s, CO, OCH₂), 3.62 (2 H, m, CH₂ OMe) and 3.34 (3 H, s, Me).

The following intermediates of formula (III) are known from the literature references indicated:

    ______________________________________                                         Z--CH.sub.2 CONHCO.sub.2 R.sup.2                                               Intemediate                     Literature                                     No.       Z         R.sup.2     ref.                                           ______________________________________                                         14        Cl        CH.sub.3    a                                              15        Br        t-Butyl     b                                              16        Cl        --CH.sub.2 CH.sub.3                                                                        c                                              17        Cl        --CH.sub.2 CH.sub.2 CH.sub.3                                                               c                                              18        Cl        --(CH.sub.2).sub.3 CH.sub.3                                                                c                                              19        Cl                                                                   iso-propyl                                                                               d                                                                    ______________________________________                                          (a) R. J. Bochis et. al J.Med.Chem 1978, 21 235.                               (b) N. J. Leonard and K. A. Cruikshank  J.Org.Chem. 1985, 50 2480              (c) M. Pianka and D. J. Pelton J.Chem.Soc. 1960, 983                           (d) G. I. Derkach and V. P. Belaya, Zh Obach. Khim, 1966, 36, 1942.      

INTERMEDIATES 20-32

The following compounds were prepared by the general procedure described for Intermediates (1) and (2), using the appropriate alcohol as starting material.

INTERMEDIATE 20 3-Amino-6-(2,3-dimethoxybenzyloxy)pyridazine

From 2,3-dimethoxybenzylalcohol (Aldrich) to give the title compound mp. 103°-106°, NMR δH(CDCl₃) 7.12-7.05 (2 H, m, 5'and 6'H); 6.91 (1 H, m, 4'H), to 6.85 (1 H, J_(AB) 9 Hz, 5 H), 6.77 (1 H, J_(AB) 9 Hz, 4 H); 5.50 (2 H, s, ArCH₂); 4.50 (2 H, brs, NH₂) and 3.89 (6 H, s, OCH₃).

INTERMEDIATE 21 3-Amino-6-(3,5-dimethoxy-4-ethoxybenzyloxy)pyridazine

From 3,5-dimethoxy-4-ethoxybenzylalcohol to give the title compound m.p. 169°-171°, NMR δH(CDCl₃) 6.89 (1 H, J_(AB) 8.8 Hz, 5 H); 6.79 (1 H, J_(AB) 8.8 Hz, 4 H); 6.70 (2 H, s, ArH); 5.38 (2 H, s, ArCH₂); 4.48 (2 H, brs, NH₂); 4.06 (2 H, q, J7 Hz, CH₂ CH₃); 3.88 (6 H, s, OCH₃) and 1.38 (3 H, t, J 7 Hz, CH₂ CH₃).

3,5-Dimethoxy-4-ethoxybenzylalcohol was prepared as follows:

a) 3,5-Dimethoxy-4-ethoxybenzaldehyde

A mixture of syringaldehyde (50 g, 0.275 mol), ethyl iodide (85.8 g, 0.55 mol) and potassium carbonate (151.7 g, 1.09 mol) in DMF (60 ml) was stirred and heated at 60°-70° for 6 h. The mixture was cooled and evaporated in vacuo then treated with water and extracted with diethyl ether. The extracts were dried (Na₂ SO₄) and evaporated to give the title compound (59 g) as a white solid, pure by tlc, and used without further purification.

b) 3,5-Dimethoxy-4-ethoxybenzylalcohol

The product from the previous reaction (59 g, 0.28 mol) was dissolved in methanol-ethanol (600 ml, 1:1) and treated with sodium borohydride (10.8 g, 0.285 mol) portionwise over 1 h. The mixture was stirred for 24 h at ambient temperature then treated slowly with water (50 ml) to provide a precipitate. The mixture was evaporated to remove organic solvents, treated with water (300 ml) and extracted with chloroform. The extracts were dried (Na₂ SO₄) and evaporated to give a white solid which was recrystallised from ether to give the title compound (26 g) as white needles.

INTERMEDIATE 22 3-Amino-6-(2-t-butylbenzyloxy)pyridazine

From 2-t-butylbenzyl alcohol to give title compound mp. 147°-9° δH(DMSO) 7.4 (2 H, m, ArH), 7.28 (2 H, m, ArH), 6.9 (1 H, J_(AB), 8 Hz, 4 H), 6.85 (1 H, J_(AB), 8 Hz, 5 H), 6.0 (2 H, brs, NH₂), 5.5 (2 H, s, CH₂), 1.4 (9 H, s, Me₃). (Alcohol prepared by LAH reduction of 2-t-butylbenzoic acid; M. Crawford and F. H. C. Stewart, J. Chem. Soc., 1952, 4444).

INTERMEDIATE 23 3-Amino-6-(2-ethylbenzyloxy)pyridazine

From 2-ethylbenzylalcohol.

Alcohol prepared from 2-ethylbenzoic acid (M. Crawford and F. H. C. Stewart, J. Chem. Soc. 1952, 4444) by reduction with LAH.

INTERMEDIATE 24 3-Amino-6-(2,5-dimethylbenzyloxy)pyridazine

From 2,5-dimethylbenzylalcohol to give title compound mp. 109°-111° C.

Alcohol prepared by LAH reduction of 2,5-dimethylbenzoic acid (Aldrich).

INTERMEDIATE 25 3-Amino-6(3,4,5-trimethylbenzyloxy)pyridazine

From 3,4,5-trimethylbenzylalcohol.

Alcohol prepared by LAH reduction of 3,4,5-trimethylbenzoic acid (G. H. Kosolapoff, J. Am. Chem. Soc. 69, 1652, 1947).

INTERMEDIATE 26 3-Amino-6-(2-phenylbenzyloxy)pyridazine

From 2-Phenylbenzylalcohol.

Alcohol prepared by LAH reduction of 2-phenylbenzoic acid (Aldrich).

INTERMEDIATE 27 3-Amino-6-(3-diethylaminobenzyloxy)pyridazine

From 3-diethylaminobenzylalcohol to give title compound mp. 115°-118° C.

δH (DMSO), 7.15 (1 H, t, 5'H), 6.95 (1 H, J_(AB), 8 Hz, 4 H), 6.85 (1 H, J_(AB), 8 Mz, 5 H), 6.75 (1 H, brs, 2'H), 6.65 (2 H, m, 4'H+6'H), 5.9 (2 H, s, NH₂), 5.25 (2 H, s, CH₂ O), 3.3 (4 H, quad, 2xCH₂ N), 1.05 (6 H, t, 2xMe).

Alcohol prepared by LAH reduction of 3-diethylaminobenzoic acid (P. Griess, Chem. Ber., 5, 1041, 1872)

INTERMEDIATE 28 3-Amino-6-(3-methylaminobenzyloxy)pyridazine

From 3-methylaminobenzylalcohol to give the title compound as a gum.

δH(DMSO) 7.1 (1 H, t, 5'H), 6.95 (1 H, J_(AB), 8 Hz, 4 H), 6.85 (1 H, J_(AB), 8 Hz, 5 H), 6.6 (2 H, m, 2 ArH), 6.45 (1 H, d, ArH), 5.95 (2 H, s, NH₂), 5.65 (1 H, brs, NH), 5.2 (2 H, s, CH₂ O), 2.65 (3 H, s, MeN).

Alcohol prepared by LAH reduction of 3-methylaminobenzoic acid (J. Houben and W. Brassert. Chem. Ber., 43, 209, 1910),

INTERMEDIATE 29 3-Amino-6-(3-methoxy-1-naphthylmethoxy)pyridazine

From 3-methoxy-1-naphthylmethanol to give the title compound mp. 167°-170° C.

δH (DMSO), 7.95 (2 H, 2 d, 2 ArH), 7.40 (3 H, m, 3 ArH), 7.30 (1 H, s, 2'H), 7.0 (1 H, J_(AB), 8 Hz, 4 H), 6.90 (1 H, J_(AB), 8 Hz, 5 H), 6.00 (2 H, s, NH₂), 5.75 (2 H, s, CH₂ O), 3.90 (3 H, s, OMe).

Alcohol prepared by LAH reduction of 3-methoxy-1-naphthoic acid (R. Lesser and G. Gad, Chem. Ber., 58B, 2551-9, 1925).

INTERMEDIATE 30 3-Amino-6-[2-(3,4,5-trimethoxyphenyl)ethoxy]pyridazine

From 2-(3,4,5-trimethoxyphenyl)ethanol to give an oil.

δH (DMSO), 6.95 (1 H, J_(AB), 8 Hz, 4 H), 6.90 (1 H, J_(AB), 8 Hz, 5 H), 6.60 (2 H, s, 2 ArH) 6.25 (2 H, brs, NH₂), 4.45 (2 H, t, CH₂ O), 3.75 (6 H, s, 3 MeO and 5 MeO), 3.58 (3 H, s, 4 MeO), 3.0 (2 H, t, CH₂).

Alcohol prepared by LAH reduction of 3,4,5-trimethoxyphenylacetic acid (Aldrich).

INTERMEDIATE 31 3-Amino-6-(2-pyridylmethoxy)pyridazine

From 2-pyridylmethanol (Aldrich) to give the title compound mp. 114°-115°. Nmr δH (d₆ -DMSO), 8.65 (1 H, d, 6'-H), 7.85 (1 H, tr of d, 5'-H), 7.55 (1 H, d, 3'-H), 7.45 (1 H, m, 4'-H), 7.10 (*1 H, J_(AB) 8.8 Hz, 4-H), 6.95 (1 H, J_(AB) 8.8 Hz, 5-H), 6.05 (2 H, s, NH₂), 5.45 (2 H, s, CH₂).

INTERMEDIATE 32 1-Amino-6-(2-furfuryloxy)pyridazine

From furfurylalcohol to give the title compound mp. 96°-99°. Nmr δH (d₆ -DMSO), 7.70 (1 H, d, 5'-H), 6.90 (1 H, J_(AB) 8.8 H_(z), 4-H), 6.85 (1 H, J_(AB) 8.8 H_(z), 5-H), 6.60 (1 H, d, 4'-H), 6.50 (1 H, s, 3'-H), 5.95 (2 H, s, NH₂), 5.30 (2 H, s, CH₂).

EXAMPLE 1 Methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

Intermediate 1 (29.1 g, 0.1 mol), and methyl N-chloroacetylcarbamate (15.15 g, 0.1 mol) were heated at 100° for 3 h with stirring under N₂ in dry 1,3-dimethyl-2-imidazolidinone (DMEU) (100 ml). The mixture was cooled, poured onto iced sodium bicarbonate solution and filtered to give a solid which was washed with water. The solid was dissolved in 5% methanol-chloroform and eluted through florosil. Evaporation gave a solid which was recrystallised from dimethylformamide and water to give the title compound as a white powder (14 g), m.p. 217°-220°, Nmr δ_(H) (d₆ -DMSO) 10.36 (1 H, br.s, NH), 7.87 (1 H, J_(AB) 8.8 Hz, 8-H), 7.85 (1 H, s, 3-H), 6.87 (1 H, J_(AB) 8.8 Hz, 7-H), 6.85 (2 H, s, PhH), 5.25 (2 H, s, CH₂), 3.79, 3.70 and 3.56 (2 H, s, OMe).

EXAMPLE 2 Ethyl N-[6-(2,5-Dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

Intermediate 2 (2.61 g, 10 mmol), 2,6-lutidine (1.04 g, 10 mmol) and ethyl N-chloroacetylcarbamate (1.66 g, 10 mmol) were heated at 100° for 3 h with stirring under N₂ in dry DMEU (10 ml). The mixture was cooled and filtered and the solid washed with water and ether then passed through florosil, eluting with 5% methanol-chloroform. Evaporation of the eluate gave a solid which was recrystallised from dimethylformamide and water to give the title compound as a white powder (1.26 g), m.p. 210°-211°, Nmr δ_(H) (d₆ -DMSO) 10.24 (1 H, br.s, NH), 7.85 (2 H, M, 3-H and 8-H), 7.10-6.86 (4 H, m, 7-H and PhH), 5.27 (2 H, s, CH₂ Ar), 4.17 (2 H, q, J 6.6 Hz, CH₂ CH₃), 3.78 and 3.73 (6 H, s, OMe) and 1.27 (3 H, t, J 6.6 Hz, CH₂ CH₃).

EXAMPLE 1 Methyl N-[6-(2,5-Dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

Intermediate 2 (12.0 g, 0.046 mol), 2,6-lutidine (4.92 g, 0.046 mol) and methyl N-chloroacetyl carbamate (6.97 g, 0.046 mol) were heated with stirring under N₂ at 100° for 4 h in dry DMEU (46 ml). The mixture was added to iced-water and then filtered to give a solid which was recrystallised from dimethylformamide and water to give the title compound as a light brown powder (2.44 g), m.p. 228°-230°, Nmr δ_(H) (d₆ -DMSO) 10.30 (1 H, br.s, NH), 7.88 (1 H, J_(AB) 8.8 Hz, 8-H), 7.85 (1 H, s, 3-H), 7.12-6.85 (4 H, m, ArH), 5.32 (2H, s, CH₂), and 3.72 and 3.69 (9H, s, OMe).

EXAMPLES 4 to 22

The following compounds were prepared by the general procedure described in Examples 1-3 by reacting the 3-amino-6-substituted pyridazines with the appropriate chloroacetylcarbamates.

(4) n-Propyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 174°-175°, Nmr δ_(H) (d₆ -DMSO) 10.25 (1H, br.s, NH). 7.87 (1 H, J_(AB) 8.8 Hz, 8-H), 7.85 (1H, s, 3-H) 6.87 (1 H, J_(AB) 8.8 Hz, 7-H), 6.85 (2 H, s, PhH), 5.26 (2 H, s, CH₂ Ar), 4.07 (2 H, t, J6 Hz, CH₂ CH₂ CH₃), 3.80 (6 H, s, OMe), 3.68 (3 H, s, OMe), 1.55 (2 H, dt, J6 Hz, CH₂ CH₂ CH₃) and 0.94 (3 H, t, J6 Hz, CH₂ CH₂ CH₃)

(5) n-Butyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 185°-187°, Nmr δ_(H) (d₆ -DMSO) 10.23 (1 H, br.s, NH), 7.85 (1 H, J_(AB) 8.8 Hz, 8-H), 7.8 (1 H, s, 3-H), 6.86 (1 H, J_(AB) 8.8 Hz, 7-H), 6.65 (2 H, s, PhH), 5.27 (2 H, s, CH₂ Ar), 4.12 (2 H, t, J 6 Hz, CH₂ CH₂ CH₂ CH₃), 3.80 (6 H, s, OMe), 3.67 (3 H, s, OMe), 1.61 (2 H, m, CH₂ CHhd 2CH₂ CH₃), 1.38 (2 H, m, CH₂ CH₂ CH₂ CH₃) and 0.92 (3 H, t, J6 Hz, CH₂ CH₂ CH₂ CH₃).

(6) n-Propyl N-[6-(2,5-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 199°-200°, Nmr δ_(H) (d₆ -DMSO) 9.93 (1 H, br.s, NH). 7.87 (2 H, m, 3-H and 8-H), 7.17-6.89 (4 H, m, 7-H and PhH), 5.42 (2 H, s, CH₂ Ar), 4.17 (2 H, t, J6 Hz, CH₂ CH₂ CH₃), 3.85 and 3.80 (6 H, s, OMe), 1.73 (2 H, dt, J6 Hz, CH₂ CH₂ CH₃) and 1.04 (3 H, t, J6 Hz, CH₂ CH₂ CH₃).

(7) Ethyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 204°-206°, Nmr δ_(H) (d₆ -DMSO) 10.25 (1 H, br.s, NH), 7.85 (1 H, J_(AB) 8.8 Hz, 8-H), 7.83 (1 H, s, 3-H) 6.85 (1 H, J_(AB) 8.8 Hz, 7-H), 6.64 (2H, s, PhH), 5.27 (2 H, s, CH₂ Ar), 4.15 (2 H, q, J6 Hz, CH₂ CH₃), 3.28 (6 H, s, OMe), 3.16 (3 H, s, OMe) and 1.25 (3 H, t, J6 Hz, CH₂ CH₃).

(8) 2-Methoxyethyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 183°-185°, Nmr δ_(H) (d₆ -DMSO) 10.36 (1 H, br.s, NH), 7.85 (1 H, J_(AB) 8.8 Hz, 8-H), 7.83 (1 H, s, 3-H), 6.85 (1 H, J_(AB) 8.8 Hz, 7-H), 6.84 (2 H, s, PhH), 5.26 (2 H, s, CH₂ Ar), 4.25 (2 H, m, COCH₂), 3.79 (6 H, s, OMe), 3.18 (3 H, s, OMe) 3.08 (2 H, m, CH₂ OMe) and 3.32 (3 H, s, CH₂ OMe).

(9) Methyl N-[6-(1-Naphthylmethyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 243°-246°, δH (d₆ DMSO) 10.05 (1 H, br.s, NH), 8.25-7.55 (9H, m, napth H and 3-H and 8-H), 6.92 (1 H, J_(AB) 8.8 Hz, 7-H), 5.92 (2 H, s, CH₂ and 3.80 (3 H, s, OMe).

(10) Methyl N-[6-(2-Methoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 241°-243°, δ_(H) (d₆ DMSO) 10.1 (1 H, br.s, NH), 7.92 (1 H, s, 3-H), 7.65 (1 H, J_(AB) 8.8 Hz, 8-H), 7.45 (1 H, d, J7 Hz, PhH), 7.35 (1 H, dd, J7 Hz, PhH), 6.95 (2 H, m, PhH), 6.72 (1 H, J_(AB) 8.8 Hz, 7-H), 5.36 (2 H, s, CH₂), 3.89 (3 H, s, OMe), and 3.77 (3 H, s, OMe).

(11) Methyl N-[6-(3,5-Dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 236°-238°, δ_(H) (d₆ DMSO) 10.30 (1 H, br.s, NH), 7.88 (1 H, J_(AB), 8.8 Hz, 8-H), 7.92 (1 H, s, 3-H), 6.90 (1 H, J_(AB) 8.8 Hz, 7-H), 6.66 (2 H, d, J0.9 Hz, 2'-H and 6'-H), 6.46 (1 H, t, J0.9 Hz, 4'-H), 5.36 (2 H, s, CH₂), 3.78 (6 H, s, OMe) and 3.70 (3 H, s, OMe).

(12) Methyl N-[6-(3-methylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 205°-208°, Nmr δ_(H) (d₆ -DMSO) 9.95 (1 H, br.s, NH), 7.85 (1 H, s, 3-H), 7.80 (1 H, J_(AB) 8.8 Hz, 8-H), 7.30 (3 H, m, 2'-H, 4'-H and 6'-H), 7.15 1 H, m, 5'-H), 6.82 (1 H, J_(AB) 8.8 Hz, 7-H), 5.80 (2 H, s, CH₂), 3.72 (3 H, s, OMe) and 2.34 (3 H, s, Me).

(13) t-Butyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 191.5°-192.5°, Nmr δ_(H) (d₆ -DMSO) 9.95 (1 H, br.s, NH), 7.85 (1 H, J_(AB) 8.8 Hz, 8-H), 7.79 (1 H, br.s, 3-H) 6.87 (1 H, J_(AB) 8.8 Hz, 7-H) 6.86 (2 H, s, PhH), 5.25 (2 H, s, CH₂), 3.79 (6 H, s, OMe), 3.68 (3 H, s, OMe) and 1.50 (9 H, s, t-Bu).

(14) Methyl N-[6-(3,4,5-trimethoxybenzylthio)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 221°-223°, Nmr δ_(H) (d₆ -DMSO) 10.51 (1 H, br.s, NH), 8.11 (1 H, s, 3-H), 7.87 (1 H, J_(AB) 8.8 Hz, 8-H), 7.17 (1 H, J_(AB) 8.8 Hz, 7-H), 6.88 (2 H, s, PhH), 4.49 (2 H, s, CH₂), 3.83 (6 H, s, OMe) and 3.70 (3 H, s, OMe).

(15) Methyl N-[6-(dimethylaminobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 200°-203°, Nmr δ_(H) (d₆ -DMSO) 10.05 (1 H, br.s, NH), 7.93 (1 H, s, 3-H) 7.90 (1 H, J_(AB) 8.8 Hz, 8-H), 7.30 (1 H, t, 5'-H), 6.95-6.80 (4 H, m, 2'-H.4'-H, 6'-H and 7-H), 5.40 (2 H, s, CH₂), 3.78 (3 H, s, MeO) and 2.98 (6 H, s, NMe₂)

(16) Methyl N-[6-(3-Methoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate m.p. 184°-189.5°, Nmr δ_(H) (CDCl₃) 10.55 (1 H, br.s, NH), 8.02 (1 H, br.s, 3-H), 7.75 (1 H, J_(AB) 8.8 Hz, 8-H), 7.32 (1 H, dd, J7.5 Hz, 5'-H), 7.07 (2 H, m, ArH), 6.88 (1 H, dd, J7.5 and 2 Hz, ArH), 6.70 (1 H, J_(AB) 8.8 Hz, 7-H), 5.34 (2 H, s, CH₂), 3.88 and 3.83 (6 H, s, OMe).

(17) Ethyl N-[6-benzyloxyimidazo[1,2-b]pyridazin-2-yl]carbamate, m.p.>211° (decomp), Nmr δ_(H) (d₆ -DMSO) 10.25 (1 H, br.s,NH), 7.87 (1 H, J_(AB) 8.8 Hz, 8-H), 7.72 (2 H, s, 3-H), 7.57-7.37 (5 H, m,Ph), 5.35 (2 H,s,CH₂ Ar), 4.15 (2 H, q, J6 Hz, CH₂ CH₃) and 1.27 (3 H, t, J6 Hz, CH₂ CH₃).

(18) Methyl N-(6-n-butylthioimidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 170°-171°, Nmr δ_(H) (d₆ -DMSO) 10.40 (1 H, br.s, NH), 7.94 (1 H, s, 3 H), 7.76 (1 H, J_(AB) 8.8 Hz, 8-H), 7.06 (1 H, J_(AB) 8.8 Hz, 7-H), 3.72 (3 H, s, OMe), 3.18 (2 H, t, J6 Hz, CH₂ S), 1.68 (2 H, m CH₂ CH₂ S), 1.44 (2 H, m, CH₂ CH₂ CH₂ S) and 0.83 (3 H, t, J6 Hz, CH₃ CH₂ CH₂ S).

(19) Methyl N-(6-benzylthioimidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 223°-225° (decomp), Nmr δ_(H) (d₆ -DMSO) 10.42 (1 H, br,s, NH), 7.99 (1 H, s, 3-H), 7.77 (1 H, J_(AB) 8.8 Hz, 8-H), 7.52-7.20 (5H, m, Ph), 7.07 (1 H, J_(AB) 8.8 Hz, 7-H), 4.45 (2 H, s, CH₂) and 3.68 (3 H, s, OMe).

(20) Methyl N-[6-(3,5-dimethoxy-4-(methoxyethoxymethoxy)benzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 149°-150°, Nmr δ_(H) (CDCl₃) 9.58 (1 H, br.s, NH), 8.02 (1 H, br.s, 3-H) 7.75 (1 H, J_(AB) 8.8 Hz, 8-H), 6.75 (1 H, J_(AB) 8.8 Hz, 7-H), 6.70 (2 H, s, 2'-H and 6'-H), 5.29 (2 H, s, CH₂), 5.18 (2 H, s, CH₂), 4.08-3.91 (2 H, m, CH₂), 3.85 (9 H, s, OMe), 3.6-3.45 (2 H, m, CH₂) and 3.35 (3 H, s, OMe).

(21) Methyl N-[6-(3-chlorobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate m.p. 268°-270°, Nmr δ_(H) (d₆ -DMSO) 10.32 (1 H, br.s, NH) 7.87 (1 H, J_(AB) 8.8 Hz, 8-H), 7.83 (1 H, s, 3-H), 7.61 (1 H, s, 2'-H), 7.53-7.41 (3 H, m, PhH), 6.91 (1 H, J_(AB) 8.8 Hz, 7-H) 5.38 (2 H, s, CH₂) and 3.68 (3 H, s, OMe).

(22) Methyl N-[6-(2-thienylmethylimidazo[1,2-b]pyridazin-2-yl]carbamate, m.p. 207°-209°, Nmr δ_(H) (d₆ -DMSO), 10.38 (1 H, br.s, NH), 7.86 (1 H, s, 3-H), 7.82 (1 H, J_(AB) 8.8 Hz, 8-H), 7.58 (1 H, d, 5'-H), 7.30 (1 H, d, 3'-H), 7.05 (1 H, t, 4'-H), 6.82 (1 H, J_(AB) 8.8 Hz, 7-H), 5.56 (2 H, s, CH₂) and 3.66 (3 H, s, CMe).

EXAMPLE 23 2,2,2-Trifluoroethyl-N-[6(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazine-2-yl]carbamate a) Ethyl 6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazine-2-carboxylate

Ethyl bromopyruvate (117 g, 0.6 mol) was added to 3-amino-6-(3,4,5-trimethoxy)pyridazine (174.6 g, 0.6 mol) and 2,6-lutidine (62.4 g, 0.6 mol) in dry DMF (600 ml) with stirring under N₂. The mixture was heated at 100° for 3 h, cooled and concentrated in vacuo then treated with water and filtered to give a brown solid which was washed with water and ether. The solid was crystallised from DMF and water to give the title compound as a crystalline solid (88 g), m.p. 159°-163°, Nmr δ_(H) (CDCl₃) 8.31 (1 H, s, 3H), 7.84 (1 H, J_(AB) 8.8 Hz, 8 H), 6.82 (1 H, J_(AB) 8.8 Hz, 7 H), 6.70 (2 H, s, ArH), 5.30 (2 H, s, CH₂ Ar), 4.45 (2 H, q, J7 Hz, OCH₂ CH₃), 3.88 (6 H, s, OCH₃), 3.86 (3 H, s, OCH₃) and 1.44 (3 H, t, J7 Hz, CH₃).

6(3,4,5-Trimethoxybenzyloxy)imidazo[1,2-b-]pyridazine-2-carboxylic acid

The product of stage (a) (1.94 g, 5 mmol) was heated under reflux with stirring with sodium hydroxide solution (1 ml, 10M, 10 mmol), water (9 ml) and methanol (5 ml) for 20 min. The mixture was cooed and acidified with dilute hydrochloric acid and filtered to give a solid powder (1.5 g), m.p. 224°-226° (decomp), Nmr δ_(H) (d₆ -DMSO) 8.56 (1 H, s, 3H), 8.07 (1 H, J_(AB) 8.8 Hz, 8H), 7.05 (1 H, J_(AB) 8.8 Hz, 7 H), 6.88 (2 H, s, ArH), 5.29 (2 H, s, CH₂ Ar), 3.82 (6 H, s, OCH₃)3.68 (3 H, s, OCH₃) and 3.32 (1 H, br.s, CO₂ H).

c) 6-(3,4,5-Trimethoxybenzyloxy)imidazo[1,2-b-]pyridazine-2-carboxylic acid azide

Oxalyl chloride (0.13 ml, 1.5 mmol) was added to the product of stage (b) (0.36 g, 1 mmol) and pyridine (0.079 g, 1 mmol) in dry benzene (5 ml) with stirring under N₂. The mixture was heated under reflux for 3 h, cooled, and evaporated in vacuo to give a grey solid:

This solid was treated with dioxan (10 ml), water (10 ml) and sodium azide (excess) and stirred vigorously overnight at ambient temperature. The mixture was filtered and the solid dried in vacuo to give the title compound as a powder (0.29 g), m.p. >139° (decomp), Nmr δH (CDCl₃) 8.35 (1 H, s, 3H), 7.85 (1 H, J_(AB) 8.8 Hz, 8 H), 6.85 (1 H, J_(AB) 8.8 Hz, 7 H), 6.70 (2 H, s, ArH), 5.31 (2 H, s, CH₂ Ar), 3.90 (6 H, s, OCH₃) and 3.88 (3H, s, OCH₃).

d) 2,2,2-Trifluoroethyl-N-[6(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b-]pyridazine-2-yl]carbamate

The product of stage (c) (2.3 g, 6 mmol), 2,2,2-trifluoroethanol (ca-3 ml) and toluene (60 ml) were heated with stirring under N₂ at reflux until t.l.c. showed complete reaction (ca 2 h.).

The mixture was cooled overnight and filtered to give a solid which was washed with ether and dried to give the title compound as a powder (0.43 g), m.p. 205°-210° (decomp.) Nmr δ_(H) (d₆ DMSO) 10.81 (1 H, br.s, NH), 7.88 (1 H, J_(AB) 8.8 Hz, 8 H), 7.85 (1 H, s, 3 H), 6.90 (1 H, J_(AB) 8 Hz, 7 H), 6.85 (2 H, s, ArH), 5.25 (2 H, s, CH₂ Ar), 4.83 (2 H, q, J9 Hz, CH₂ CF₃), 3.76 (6 H, s, OCH₃) and 3.65 (3 H, s, OCH₃).

EXAMPLE 24 2-Hydroxyethyl-N-[6(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

A similar procedure was followed to that described in Example 23(d) except that the crude product was chromatographed on SiO₂ eluting with 5% methanol-chloroform with subsequent recrystallisation from DMF-water to yield the title compound as a powder, m.p. 193°-5°, NMR δ_(H) (d₆ DMSO) 10.35 (1 H, br.s, NH) 7.85 (1 H, J_(AB), 8.8 Hz, 8 H), 7.83 (1 H, s, 3 H), 6.86 (1 H, J_(AB) 8.8 Hz, 3 H), 6.84 (2 H, s, ArH), 5.25 (2 H, s, CH₂ Ar), 4.82 (1 H, t, J4 Hz, OH), 4.15 (2 H, m), 3.80 (6 H, s, OCH₃) and 3.66 (5 H, m, OCH₂ and OCH₃).

EXAMPLE 25 2-(1-morpholino)ethyl-N-[6(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin 2-yl]carbamate

A similar procedure was followed to that described in Example 23(d) except that the crude product was chromatographed on SiO₂ eluting with 5% methanol-chloroform and boiled with a little ethanol to give the title compound as a powder, m.p. 161°-162°, Nmr δH (d₆ DMSO) 10.30 (1 H, br.s, NH), 7.88 (1 H, s, 3 H), 7.85 (1 H, J_(AB), 8.8 Hz 8 H), 6.87 (1 H, J_(AB), 8.8 Hz, 7 H), 6.85 (2 H, s, ArH), 5.26 (2 H, s, CH₂ Ar), 4.22 (2 H, t, J5 Hz, CO.OCH₂ 3.80 (6 H, s, OCH₃), 3.68 (3 H, s, OCH₃), 3.58 (4 H, m, CH₂ OCH₂), 2.59 (2 H, t, J5 Hz, CO.OCH₂ CH₂ N) and 2.45 (4 H, m, CH₂ NCH₂).

EXAMPLE 26 Methyl N-[N-Methyl-6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

Sodium hydride (1.26 g, 60%, 31.5 mMol) was added portionwise to a stirred suspension of methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]-pyridazin-2, -yl]carbamate (9.51 g, 24.5 mMol) in DMEU (100 ml) under N₂ at ambient temperature. The mixture was treated with iodomethane (4.9 g 2.15 ml, 35 mMol) and after a further 1 hour the mixture was treated with molar equivalents of sodium hydride and iodomethane. After 2 hours the mixture was poured into water (100 ml) and was filtered to give a white solid which was chromatographed on SiO₂ eluting with 2% methanol chloroform. The product was recrystallised from DMF and water to yield the title compound as a white powder (8.29 g), m.p. 177°-178° C., NMR δH (d₆ DMSO) 8.04 (1 H, s, 3 H), 7.96 (1 H, J_(AB) 8.8 Hz, 8 H), 6.92 (1 H, J_(AB) 8.8 Hz, 7 H), 6.86 (2 H, s, ArH), 5.25 (2 H, s, CH₂), 3.79 (9 H, s, OCH₃), 3.68 (3 H, s, CO.OCH₃) and 3.42 (3 H, s, NCH₃).

EXAMPLE 27 Methyl N-[N-ethyl-6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]-carbamate

A similar procedure was followed as described in Example 26 to give the title compound as a white solid, m.p. 153°-155° C., NMR δH (d₆ DMSO), 8.04 (1 H, s, 3 H), 7.96 (1 H, J_(AB), 8.8 Hz, 8 H), 6.92 (1 H, J_(AB), 8.8 Hz, 7 H), 3.66 (3 H, s, NCH₃) and 1.19 (3 H, t, CH₂ CH₃).

EXAMPLE 28 2,3-Dihydroxypropyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

The product of Example 23(c) was reacted with solketal using a similar procedure to that described in Example 23(d) except that upon completion of the reaction between the acyl azide and solketal the crude mixture was evaporated in vacuo and then heated at 60°-70° C. for 0.5 hours with dilute hydrochloric acid and ethanol. The reaction mixture was neutralised with sodium bicarbonate solution, evaporated in vacuo and chromatographed on n SiO₂ eluting with 7% methanol-chloroform to give the title compound as a white solid, m.p. 175°-176° C., NMR δH (d₆ DMSO) 10.28 (1 H, brs, NH), 7.88 (1 H, J_(AB) 8.8 Hz, 8 H), 7.86 (1 H, s, 3 H), 6.87 (1 H, J_(AB) 8.8 Hz, 7 H), 6.85 (2 H, s, ArH), 5.28 (2 H, s, ArCH₂), 4.90 (1 H, d, J4 Hz, 2'-OH), 4.65 (1 H, t, J4 Hz, 1'-OH), 4.20-4.0 (2 H, m, CO.OCH₂), 3.80 (6 H, s, OCH₃), 3.80-3.70 (1 H, m, HO-CH), 3.69 (3 H, s, OCH₃) and 3.40 (2 H, t, J4 Hz, HOCH₂).

EXAMPLE 29 2-Dimethylaminoethyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]-pyridazin-2-yl]carbamate

The product of Example 23(c) was treated with (2-dimethylamino)ethanol using a similar procedure to that described in Example 23(d) except that the crude product was chromatographed on SiO₂ eluting with 5% methanol-chloroform to give a solid which was washed with ethanol and dried to give the title compound as a white powder, m.p. 185°-186° C., NMR δH (d₆ DMSO) 10.32 (1 H, brs, NH), 7.88 (1 H, J_(AB), 8.8 Hz, 8 H), 7.85 (1 H, s, 3 H), 6.89 (1 H, J_(AB), 8.8 Hz, 7 H), 6.85 (2 H, s, ArH), 5.77 (2 H, s, ArCH₂), 4.60 (2 H, t, J4 Hz, CO.OCH₂), 3.80 (6 H, s, OCH₃), 3.69 (3 H, s, OCH₃), 2.50 (2 H, t, CH₂ N) and 2.21 (6 H, s, NMe₂).

EXAMPLE 30 Phenyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

The product of Example 23(c) was reacted with phenol using a similar procedure to that described in Example 23(d) except that the crude product was chromatographed on SiO₂ eluting with 5% methanol-chloroform to give a solid which was washed with acetonitrile and dried to give the title compound as a white powder, m.p. 210°-213° C., NMR δH(CDCl₃) 10.12 (1 H, brs, NH), 8.05 (1 H, s, 3 H), 7.80 (1 H, J_(AB), 8.8 Hz, 8 H), 7.55-7.15 (5 H, m, Ph), 6.69 (2 H, s, ArH), 6.67 (1 H, J_(AB), 8.8 Hz, 7 H), 5.28 (2 H, s, ArCH₂) and 3.9 (9 H, s, OCH₃).

EXAMPLE 31 3-Amino-6-(2bromo-3,4,5-trimethoxybenzyloxy)pyridazine

a) 3-Amino-6-(3,4,5-trimethoxybenzyloxy)pyridazine (Intermediate 1, 2.91 g, 10 mMol) in acetic acid (20 ml) was treated dropwise with a solution of bromine (1.59 g, 10 mMol) in acetic acid (2 ml) over 5 minutes. After 0.5 hours, the mixture was filtered to give a cream solid which was suspended in water and basified with sodium hydroxide solution. The mixture was extracted with chloroform and the extracts were washed with water, dried (Na₂ SO₄) and evaporated in vacuo to yield a cream solid which was recrystallised from toluene to give the title compound (2.76 g) as cream needles, m.p. 160°-161° C., NMR δH (CDCl₃) 6.93 (1 H, s, ArH), 6.91 (1 H, J_(AB), 8.8 Hz, 5 H), 6.80 (1 H, J_(AB), 8.8 Hz, 4 H), 5.49 (2 H, s, CH₂), 4.95 (2 H, brs, NH₂), 3.91 (3 H, s, OCH₃), 3.90 (3 H, s, OCH₃) and 3.89 (3 H, s, OCH₃).

b) Methyl N-[6-(2-bromo-3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

A similar procedure was followed to that described in Examples 1-3 to give the title compound as a white powder, m.p. 218°-219° C., NMR δH (CDCl₃) 9.45 (1 H, brs, NH), 8.03 (1 H, brs, 3 H), 7.75 (1 H, J_(AB), 8.8 Hz, 8 H), 6.94 (1 H, s, ArH), 6.75 (1 H, J_(AB), 8.8 Hz, 7 H), 5.40 (2 H, s, ArCH₂) and 3.96-3.86 (12 H, m, OCH₃).

EXAMPLES 32-35

The following compounds were prepared using a similar procedure to that described in Examples 1-3:

EXAMPLE 32 Methyl N-[6-(2,3-dimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 210°-211° C., NMR δH d₆ (DMSO) 10.35 (1 H, brs, NH), 7.86 (1 H, J_(AB), 8.8 Hz, 8 H), 7.84 (1 H, s, 3 H), 7.10 (3 H, s, PhH), 6.88 (1 H, J_(AB), 8.8 Hz, 7 H), 5.35 (2 H, s, CH₂), and 3.86, 3.80 and 3.72 (9 H, s, OCH₃).

EXAMPLE 33 Methyl N-[6-(3,5-dimethoxy-4-ethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 190°-193°, NMR δH (d₆ DMSO) 10.33 (1 H, brs, NH), 7.88 (1 H, J_(AB), 8.8 Hz, 8 H), 7.85 (1 H, s, 3 H), 6.88 (1 H, J_(AB), 8.8 Hz, 7 H), 6.85 (2 H, s, ArH), 5.77 (2 H, s, ArCH₂, 3.90 (2 H, q, J7 Hz, CH₂ CH₃), 3.80 (60 H, s, ArOCH₃), 3.69 (3 H, s, CO.OCH₃) and 1.24 (3 H, t, J7 Hz, CH₂ CH₃).

EXAMPLE 34 Methyl N-[6-(2-t-butylbenzyloxy)imidazo [1,2-b]pyridazin-2-yl]carbamate

m.p. 220°-223° δH(DMSO) 9.95 (1 H, brs, NH), 7.85 (1 H, s, 3 H), 7.8 (1 H, J 8 Mz, 8 H), 7.5 (2 H, m, ArH), 7.28 (2 H, m, ArH), 6.8 (1 H, J_(AB) 8 Hz, 7 H), 5.5. (2 H, s, CH₂), 3.7 (3 H, s, OMe), 1.4 (9 H, s, Me₃).

(From Intermediate 22).

EXAMPLE 35 Methyl N-[6-(2-ethylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 190°-191° δH (DMSO) 9.95 (1 H, brs, NH), 7.85 (1 H, s, 3 H), 7.8 (1 H, J 8 Hz, 8 H), 7.45 (1 H, d, ArH), 7.3 (3 H, m, ArH), 6.8 (1 H, J_(AB) 8 Hz, 7 H), 5.4 (2 H, s, O--CH₂), 3.7 (3 H, s, OMe), 2.7 (2 H, quad, CH₂), 1.2 (3 H, t, Me).

(From Intermediate 23).

EXAMPLE 36 n-Propyl N-[6-(2,5-dimethylbenzyloxy)imidazo[1,2-b]pyridazin--2-yl]carbamate

m.p. 196°-7° δH (DMSO) 9.85 (1 H, brs, NH), 7.85 (1 H, s, 3 H), 7.80 (1 H, J 8 Hz, 8 H), 7.25 (1 H, s, 6'H), 7.1 (2 H, 2 d, 3'H and 4'H), 6.8 (1 H, J_(AB) 8 Hz, 7 H), 5.35 (2 H, s, OCH₂), 4.1 (2 H, t, OCH₂), 2.3 (6 H, 2 s, 2×ArMe), 1.7 (2 H, quad, CH₂), 0.95 (3 H, t, Me).

(From n-propylchloroacetylcarbamate and Intermediate 24).

EXAMPLE 37 Methyl N-[6-(3,4,5-trimethylbenzyloxy)imidazo[2,1-b]pyridazin-2-yl]carbamate

m.p. 227°-229° δH (DMSO) 9.90 (1 H, brs, NH), 7.85 (1 H, s, 3 H), 7.75 (1 H, J_(AB) 8 Hz, 8 H), 7.15 (2 H, s, ArH), 6.80 (1 H, J_(AB) 8 Hz, 7 H), 5.25 (2 H, s, OCH₂), 3.7 (3 H, s, OMe), 2.28 (6 H, s, 2×ArMe), 21.5 (3 H, s, ArMe).

(From Intermediate 25).

EXAMPLE 38 Methyl N-[6-(2-phenylbenzyloxy)imidazo-[1,2-b]pyridazin-2-yl carbamate

m.p. 203°-204. δH (DMSO) 9.92 (1 H, brs, NH), 7.75 (1 H, J_(AB) 8 Hz, 8 H), 7.70 (1 H, s, 3) 7.4 (9 H, m, 9 ArH), 6.75 (1 H, J_(AB) 8 Hz, 7 H), 5.3 (2 H, s, OCH₂), 3.7 (3 H, s, OCH₃).

From Intermediate 26).

EXAMPLE 39 Methyl N-[6-(3-diethylaminobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate hydrochloride

m.p. 220°-225° δH (DMSO), 10.35 (1 H, brs, NH), 7.9 (1 H, J_(AB) 8 Hz, 8 H), 7.8 (1 H, s, 3 H), 7.6 (4 H, m, 4×ArH), 6.9 (1 H, J_(AB) 8 Hz, 7 H), 5.4 (2 H, s, CH₂ O), 3.7 (3 H, s, OMe) 3.5 (4 H, brs, 2×CH₂ N), 1.05 (6 H, t, 2×Me).

From Intermediate 27).

EXAMPLE 40 Methyl N-[6-(3-methylaminobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate hydrochloride

m.p. 213°-215° (dec) δH (DMSO) 10.4 (1 H, brs, NH), 7.9 (1 H, J_(AB) 8 Hz, 8 H), 7.85 (1 H, s, 3 H), 7.3 (4 H, m, 4 ArH), 6.9 (1 H, J_(AB) 8 Hz, 7 H), 5.4 (2 H, s, CH₂ O), 3.7 (3 H, s, OMe), 2.85 (3 H, s, MeN).

(From Intermediate 28).

EXAMPLE 41 Ethyl N-[6-(3-dimethylaminobenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 204°-8° δH (DMSO) 9.95 (1 H, brs, NH), 7.85 (1 H, s, 3 H), 7.80 (1 H, J 8 Hz, 8 H), 7.2 (1 H, t, 5'H), 6.85 (1 H, J_(AB) 8 Hz, 7 H), 6.75 (3 H, m, 3 ArH), 5.3 (2 H, s, CH₂ O), 4.2 (2 H, quad, OCH₂), 2.9 (6 H, s, Me₂ N), 1.25 (3 H, t, Me).

EXAMPLE 42 Ethyl N-[6-(1-naphthylmethoxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 240°-245° δH (DMSO), 10.0 (1 H, bs, NH), 8.2 (1 H, m, ArH), 8.05 (2 H, m, 2 ArH), 7.95 (1 H, s, 3 H), 7.90 (1 H, J_(AB) 8 Hz, 8 H), 7.85 (1 H, d, 2'H), 7.65 (3 H, m, 3 ArH), 6.90 (1 H, J_(AB) 8 Hz, 7 H), 5.95 (2 H, s, CH₂ O), 4.25 (2 H, quad. OCH₂), 1.35 (3 H, t, Me).

(From Intermediate 3)

EXAMPLE 43 n-Propyl N-[6-(1-naphthylmethoxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 208°-210° δH (DMSO), 10.25 (1 H, brs, NH), 8.15 (1 H, m, ArH), 8.00 (2 H, m, 2 ArH), 7.90 (1 H, s, 3 H), 7.85 (1 H, J_(AB) 8 Hz, 8 H), 7.75 (1 H, d, 2'H), 7.60 (3 H, m, 3 ArH), 6.85 (1 H, J_(AB) 8 Hz, 7 H), 5.8 (2 H, s, OCH₂), 4.1 (2 H, t, OCH₂), 1.65 (2 H, m, CH₂), 0.9 (3 H, t, Me).

(From Intermediate 3).

EXAMPLE 44 Methyl N-[6-(3-methoxy-1-naphthylmethoxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

δH(DMSO) 10.0 (1 H, brs, NH), 8.1 (1 H, d, ArH), 7.9 (2 H, m, ArH+3H), 7.85 (1 H, J_(AB) 8 Hz, 8 H), 6.85 (1 H, J_(AB) 8 Hz, 7 H), 5.8 (2 H, s, CH₂ O), 3.90 (3 H, s, OMe), 3.7 (3 H, s, OMe).

(From Intermediate 29).

EXAMPLE 45 Methyl N-[6-[2-[3,4,5-trimethoxyphenyl)ethoxy]imidazo[1,2-b]pyridazin-2-yl]carbamate

m.p. 203°-6° δH (DMSO) 9.95 (1 H, brs, NH), 7.80 (1 H, s, 3 H), 7.75 (1 H, J_(AB) 8 Hz, 8 H), 6.8 (1 H, J_(AB) 8 Hz, 7 H), 6.65 (2 H, s, 2 ArH), 4.5 (2 H, t, CH₂ O), 3.8 (6 H, s, 3 MeO, 5 MeO), 3.7 (3 H, s, OMe), 3.65 (3 H, s, 4 MeO), 3.0 (2 H, t, CH₂).

(From Intermediate 30).

EXAMPLE 46 Methyl N-6-(3,4,5-trimethoxyphenethyl)imidazo[1,2-b]pyridazin-2-ylcarbamate a) 4-Oxo-6-(3,4,5-trimethoxyphenethyl)hex-5-enoic acid

A solution of laevulinic acid (50 g, 0.43 mol) in water (200 ml) was added to a mixture of 3,4,5-trimethoxybenzaldehyde (85 g, 0.43 mol) in ethanol (150 ml) and sodium hydroxide solution (5%, 700 ml). The mixture was warmed with vigorous stirring until all the aldehyde had dissolved and was then poured onto ice (ca 2 Kg). It was then acidified to pH3-4 and left overnight. The crystalline material formed was filtered off, dried in vacuo and then recrystallised from ethanol to give pale yellow crystals (30.08 g), m.p. 187°-9°.

N.m.r. δH (d₆ -DMSO), 7.57 (1 H, d, J_(A1B1) =18.0 Hz, CH), 7.08 (2 H, s, 2'H, 6'H), 6.91 (1 H, d, J_(AB) =18.0 Hz, CH), 3.83 (6 H, s, 3'-MeO and 5'MeO), 3.70 (1 H, s, 4'MeO), 3.33 (1 H, br. m. unres, CO₂ H), 2.92 (2 H, t, J_(A2B2) =7.0 Hz, CH₂) and 2.50 2 H, t, J_(A2B2) =7.0 Hz, CH₂).

b) 4,5-dihydro-6-(3,4,5-trimethoxy-α-styryl)pyridazin-3(2H)-one

4-Oxo-6-(3,4,5-trimethoxyphenethyl)hex-5-enoic acid (20 g, 0.068 mol) was dissolved in glacial acetic acid (240 ml) and then hydrazine hydrate (3.4 g, 0.068 mol) was added. The mixture was heated under reflux for 2.5 h, cooled and poured into water (ca 21). After standing overnight, the crystals formed were filtered at the pump and dried in vacuo to give the product (13.58 g). A portion (3.5 g) was recrystallised from methanol and gave pale yellow crystals (3.18 g). m.p. 173°-5°.

N.m.r. δH(CDCl₃), 8.91 (1H, brs, NH), 6.82 (2 H, s, CH, CH), 6.70 (2 H, s, CH, CH), 3.89 (6 H, s, 3'-MeO and 5'-MeO), 3.87 (3 H, s, 4'MeO), 2.82 (2 H, t, J_(AB) =9.0 Hz) and 2.56 (2 H, t, J_(AB) =9.0 Hz).

c) 4,5-Dihydro-6-(3,4,5-trimethoxyphenethyl)pyridazin-3(2H)-one

4,5-Dihydro-6-(3,4,5-trimethoxy-α-styryl)pyridazin-3(2H)-one (5 g, 0.017 mol) was hydrogenated (85°, 10 atm H₂) on glacial acetic acid (150 ml) in the presence of 10% Pd/C catalyst (0.25 g until the requisite uptake of hydrogen had occurred. The mixture was then filtered through Hyflo, and the filtrate evaporated in vacuo at 35°. The remaining traces of glacial acetic acid were removed by azeotroping with toluene and the brown solid (4.9 g) purified further by silica gel chromatography, with 1% methanol/dichloromethane as the eluent. Removal of the solvent from the appropriate fractions gave the product as a white solid (3.04 g), m.p. 116°-117°.

N.m.r δH(CHCl₃), 8.46 (1 H, s, br, NH), 6.43 (2 H, s, 2'H, 6'H), 3.83 (6 H, s, 3'MeO and 5'MeO), 3.81 (3 H, s, 4'MeO), 2.84 (2 H, t, J_(AB) =7 Hz, CH₂), 2.61 (2 H, t, J_(AB) =7 Hz) and 195 (4 H, m, part. res, CH₂, CH₂).

d) 6-(3,4,5-Trimethoxyphenethyl)pyridazin-3(2H)-one

4,5-Dihydro-6-(3,4,5-trimethoxyphenethyl pyridizan-3(2H)-one (1.72 g, 5.93 m mol) and selenium dioxide (0.98 g, 8.83 m mol) was refluxed in ethanol (80 ml) for 4.5 days. More selenium dioxide (0.5 g, 4.51 m mol) was added and the mixture was refluxed for a further 5 days. The mixture was filtered to remove selenium which had separated and the filtrate evaporated in vacuo to give a brown sticky solid (2.21 g). This solid was subjected to flash chromatography on silica with 1-2% methanol-dichloromethane as the eluant. Combination of the appropriate fractions gave the product as a sandy-brown crystalline solid (1.43 g), m.p. 122°-4°.

N.m.r. δH (CDCl₃) 11.64 (1 H, brs, NH), 7.08 (1 H, d, J_(AB) =6 Hz, HetCH), 6.89 (1 H, d, J_(AB) =6 Hz, HetCH), 6.48 (2 H, s, 2'H, 6'H), 3.83 (9 H, 2 s, 3'MeO and 5'MeO, 4'MeO) and 2.82 (4 H, s, CH₂ --CH₂).

e) 3-Chloro-6-(3,4,5-trimethoxyphenethyl)pyridazine

A mixture of 6-(3,4,5-Trimethoxyphenethyl)pyridazin-3(2H)-one (2.80 g; 9.65 mmol) and phosphorus oxychloride (70 ml) was heated at 100° for 1 h, cooled to room temperature and hydrolysed by careful, gradual addition to water over 3 h, so that the temperature did not exceed 30°. The mixture was then basified to pH12 by the addition of sodium hydroxide solution (1N, 700 ml) and then left at 4° overnight. The precipitate was filtered at the pump, washed well with water to remove inorganic salts and the residue on the sinter taken up on dichloromethane. After drying (sodium sulphate), removal of the solvent gave a light-brown solid (2.84 g) which was purified by `flash` chromatography on silica, with 10% of ethyl acetate/dichloromethane as the eluent. Appropriate fractions were combined to give a white solid (2.16 g), m.p. 105°-106°.

N.m.r. δH (CDCl₃) 7.38 (1 H, d, J_(AB) =9 Hz, HetCH), 7.16 (1 H, d, J_(AB) =9 Hz, HetCH), 6.37 (2 H, s, 2'H), 3.82 (9 H, s, 3'MeO, 4'MeO and 5'MeO), 3.37 (2 H, t, J_(A2B2) =9H, CH₂), and 3.04 (2 H, t, J_(A2B2), 9HzCH₂).

f) 3-Amino-6-(3,4,5-trimethoxyphenethyl)pyridazine

3-Chloro-6-(3,4,5-trimethoxyphenethyl)pyridazine (1.97 g, 6.38 mol) in methanolic ammonia (saturated, 800 ml) was heated in a stainless steel autoclave at 150° for 65 h and then allowed to cool. The mixture was then evaporated, in vacuo to give a dark-brown sticky solid (2.84 g), which was subjected to flash chromatography on silica with 3% methanol/dichloromethane as the eluent. Combination of the relevant fractions afforded the product as a white solid (0.56 g), m.p. 130°-132°.

N.m.r. δH (CDCl₃) 6.96 (1 H, d, J_(AB) =9.0 Hz, HetCH), 6.67 (1 H, br, d, J_(AB) =9.0 Hz, HetCH), 6.42 (2 H, s, 2'H, 6'H), 4.74 and 1.98 (2 H, brs, --NH₂), 3.83 (9 H, s, 3'MeO, 4'MeO 5'Meo), 3.13 (2 H, part res m., CH₂) and 3.01 (2 H part res. m., CH₂).

g) Methyl N-6-(3,4,5-trimethoxyphenethyl)imidazo[1,2-b-]pyridazin-2-yl carbamate

3-Amino-6-(3,4,5-trimethoxyphenethyl)pyridazine (0.50 g, 1.73 mmol) and methyl N-chloroacetylcarbamate (0.26 g; 1.74 mmol) were heated in dry hexamethylphosphoramide (distilled from CaH₂ in vacuo, 15 ml) with stirring for 4 h at 100° C. under nitrogen. The mixture was then cooled, poured into water (150 ml), whereupon a precipitate formed. After standing overnight the precipitate was filtered off and dried in vacuo to yield a cream-coloured crystalline solid (0.53 g). This was purified further by flash chromatography (silica, 1-2% methanol/dichloromethane as eluent) and crystallisation from ethyl acetate to give off-white crystals (0.18 g), m.p. 175°-6°.

N.M.R. δH (CDCl₃) 10.17 (1 H, br.s, NH), 8.18 (1 H, br.s, Het 3-H); 7.77 (1 H, d, JAB=10 Hz, Het CH), 6.85 (1 H, d, JAB=10 Hz, HetCH). 6.42 (2 H, s, 2'-H,6'-H), 3.88 (3 H, s, CO₂ Me) and 3.82 (9 H, s, 3-MeO, 4'-MeO, 5'-MeO), 3.12 (2 H, part.res.m, CH₂) and 3.02 (2 H, part.res.m.CH₂).

EXAMPLE 47 Methyl N-6-(3,4,5-trimethoxy-α-styryl)imidazo[1,2-b]pyridazin-2-ylcarbamate a) 6-(3,4,5-trimethoxy-α-styryl)pyridazin-3(2H)-one

The compound of Example 46(b) (10.,0 g, 34.4 mmol) and selenium dioxide (10 g, 90.1 mmol) were heated under reflux in ethanol (300 ml) for 80 h. A further charge of selenium dioxide (10 g) was added and the reflux continued for a further 40 h. The reaction mixture was then filtered through `Hyflo`, evaporated and the residue dried in vacuo to give a dark-brown sticky solid (14.48 g). This was then chromatographed on silica with 1-2% methanol/dichloromethane. Combination of the appropriate fractions, followed by crystallisation from methanol afforded the product as a sandy-brown solid (5.57 g), m.p. 194°-196° C.

N.M.R. δh (CDCl₃) 11.95 (1 H, br.s, NH), 7.66 (1 H, d, J_(A).sbsb.1.spsb.B.sbsb.1 -10 Hz, Het CH), 7.10 (1 H, d, J_(A).sbsb.2.spsb.B.sbsb.2 -18 Hz, CH), 7.01 (1 H, d, J_(A).sbsb.1.spsb.B.sbsb.1 -10 Hz, HetCH), 6.92 (1 H, d, J_(A).sbsb.A.spsb.B.sbsb.2 -18 Hz, CH), 6.74 (2 H, s, 2'-H, 6'-H), 3.91 (6 H, s, 3'-MeO, 5'-MeO) and 3.88 (3 H, 4'-MeO).

b) 3-Chloro-6-(3,4,5-trimethoxy-α-styryl)pyridazine

6-(3,4,5-trimethoxy-α-styryl)pyridazin-3(2H)-one (5.3 g, 0.018 mol) in phosphorus oxychloride (150 ml) was heated at 100° for 1.25 h. The mixture was then added to water (31) over 2 h, keeping the temperature in the range 10°-30° C. The mixture was then carefully basified to pH10 with sodium hydroxide solution (10N, 1.31). After standing overnight, the precipitate was filtered off and dried in vacuo to give the product as a sand-brown solid (6.24 g). A portion recrystallised from ethanol had m.p. 162°-163° C.

N.m.r. δh (CDCl₃) 7.64 (1 H, d, J_(A).sbsb.1.spsb.B.sbsb.1 -10 Hz, Het CH), 7.54 (1 H, d, J_(A).sbsb.2.spsb.B.sbsb.2 -18 Hz, CH), 7.48 (1 H, d, J_(A).sbsb.1.spsb.B.sbsb.1 -10 Hz, Het CH), 7.27 (1 H, d, J_(A).sbsb.2.spsb.B.sbsb.2 -18 Hz, CH), 6.82 (2 H, s, 2'-H, 6'-H), 3.92 (6 H, s, 3'-MeO and 5'-MeO) and 3.88 (3 H, s, 4'-MeO).

(c) 3-Amino-6-(trimethoxy-α-styryl)pyridazine

3-Chloro-6-(3,4,5-trimethoxy-α-styryl)pyridazine (5.5 g, 17.1 mmol) in methanolic ammonia (saturated, 800 ml) was heated in a stainless steel autoclave at 150° C. for 100 h and then allowed to cool. Removal of the solvent and chromatography on silica (2% methanol/dichloromethane) afforded the product as a light-brown solid (1.58 g), m.p. 139°-142°

N.m.r. δh (CDCl₃) 7.49 (1 H, d, J_(A).sbsb.1.spsb.B.sbsb.1 -10 Hz CH), 7.24 (2 H, 2×superimposed d, J_(A).sbsb.1.spsb.B.sbsb.1, J_(A).sbsb.2.spsb.B.sbsb.2 =(10 Hz, 2×CH), 6.75 (3 H, d superimposed on s, J_(A).sbsb.2.spsb.B.sbsb.2 -10 Hz, CH, 2-H, 6'-H) 4.85 (2 H, br.s, NH₂), 3.92 (6 H, s, 3-MeO and 5-MeO) and 3.87 (3 H, s, 4-MeO).

Methyl N-6-(3,4,5-trimethoxy-α-styryl)imidazo[1,2-b]pyridazin-2-yl carbamate

3-Amino-6-(3,4,5-trimethoxy-α-styryl)pyridazine (1.36 g, 4.72 mmol) and methyl N-chloroacetylcarbamate (0.68 g, 4.49 mol) were heated in dry hexamethylphosphoramide (distilled form CaH₂ in vacuo 30 ml) with stirring for 4 h at 100°. The mixture was then cooled and poured into water (40 ml). The precipitate which formed was filtered off and dried in vacuo to give a yellow-brown solid (1.0 g). This was chromatographed on silica to give the product as a pale yellow solid (0.4 g), m.p. 217°-9°.

N.m.r. δH(d₆ -DMSO) 10.49 (1 H, br.s, NH), 7.99 (1 H, s, Het 3-H), 7.94 (2 H, d, JA₁ B₁ -10 Hz, HetCH), 7.60 (2 H, d, JA₂ B₂ -18 Hz, CH), 7.58 (2 H, d, JA₁ B₁ -10 Hz, HetCH), 7.28 (2 H, d, JA₂ B₂ -18 Hz, CH), 7.04 (2 H, s, 2'H, 6'H), 3.87 (6 H, s, 3'-MeO and 5'-MeO), [3.72 (3 H, s) and 3.70 (2 H, s)] (CO₂ Me and

EXAMPLE 48 Methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

6-(3,4,5-Trimethoxybenzyloxy)imidazo[1,2-b]pyridazine-2-carboxylic acid azide (Example 23C) (1.0 g, 2.6 mmol) was heated under reflux for 24 h in toluene (20 ml) and methanol (ca 1.5 ml). The mixture was cooled and evaporated in vacuo to give a yellow solid which was recrystallised from DMF and water to yield the title product (1.05 g), mp. 213°-215° and NMR identical to the product of Example 1.

EXAMPLE 49 Methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate a) 2-Amino-6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazine trifluoroacetate

t-Butyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate (Example 13, 0.43 g, 1 mmol) was dissolved in dichloromethane (2 ml) and treated with trifluoroacetic acid (1 ml). After 2 h at ambient temperature the mixture was evaporated in vacuo to give a brown oil which was triturated with diethyl ether to give the title compound (0.25 g) as a cream solid, m.p. 150°-157°, NMR δ_(H) (DMSO) 8.0 (1 H, J_(AB) 8.8 Hz, 8 H), 7.48 (1 H, s, 3 H), 7.16 (1 H, J_(AB) 8.8 Hz, 7 H), 6.44 (2 H, s, CH₂), 4.5 (brs, NH₃), 3.89 (6 H, s, OMe) and 3.75 (3 H, s, OMe).

b) Methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazine-2-yl]carbamate

The product of stage (a) (1.0 g, 3.03 mmol) was suspended in dichloromethane and shaken with dilute sodium hydroxide solution. The organic phase was dried (Na₂ SO₄) and evaporated to give a brown oil which was dissolved in dichloromethane and treated, with stirring, with triethylamine (0.42 ml, 3.03 mmol), methyl chloroformate (0.23 ml, 3.03 mmol) and 4-dimethylaminopyridine (18 mg, 0.3 mmol). The mixture was stirred at ambient temperature for 17 h then heated under reflux for 2 h and evaporated in vacuo. The resulting solid was partioned between chloroform and water, the organic phase was separated, dried (Na₂ SO₄) and evaporated to give a solid which was chromatographed on SiO₂ eluting with 2% methanol-chloroform. The product was recrystallised from DMF-H₂ O to give the title compound (0.27 g), mp. 210°-212°, NMR identical to the product of Example 1.

EXAMPLES 50-52

The following compounds were prepared using a similar procedure to that described in Examples 1-3:

EXAMPLE 50 Methyl N-[6-(2,5-Dimethylbenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

mp. 208°-209° Nmr δH (d₆ -DMSO), 10.05 (1 H, br.s, NH), 7.95 (1 H, J_(AB) 8.8 Hz, 8 H), 7.85 (1 H, s, 3-H), 7.35 (1 H, s, 6'-H), 7.20 (2 H, J_(AB) 8.8 Hz, 7 H+d, 3' or 4'-H), 6.90 (1 H, d, 3' or 4'-H), 5.90 (2 H, s, CH₂), 3.80 (3 H, s, OMe), 2.4 (3 H, s, Me), 2.35 (3 H, s, Me).

(From Intermediate 24).

EXAMPLE 51 Methyl N-[6-(2-pyridylmethoxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

mp. 231°-233° (dec) Nmr δH (d₆ -DMSO), 9.95 (1 H, br.s, NH), 8.55 (1 H, d, 6'-H), 7.85 (3 H, m, 8-H+3-H+5'-H), 7.55 (1 H, d, 3'-H), 7.35 (1 H, m, 4'-H), 6.90 (1 H, J_(AB) 8.8 H_(z), 7-H), 5.45 (2 H, s, CH₂), 3.70 (3 H, s, OMe).

(From Intermediate 31).

EXAMPLE 52 Methyl N-[6-(2-furfuryloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate

mp. 220°-224° Nmr δ_(H) (d₆ -DMSO), 10.05 (1 H, br.s, NH), 7.95 (1 H, s, 3-H), 7.90 (1 H, J_(AB) 8.8 H_(z), 8-H), 7.75 (1 H, brs, 5'-H), 6.90 (1 H, J_(AB) 8.8 H_(z), 7-H), 6.75 (1 H, d, 4'-H), 6.55 (1 H, br.s, 3'-H), 5.45 (2 H, s, CH₂), 3.80 (3 H, s, OMe).

(From Intermediate 32).

BIOLOGICAL TEST RESULTS A) Tubulin Polymerisation Assay Materials and Methods

1. Preparation of tubulin

    ______________________________________                                         a)   Fresh horse brain -                                                       b)   Buffers:                                                                  BBG.   BB          BB2G                                                        ______________________________________                                         100 mM MES*/NaOH   As BBG but   As BBG but                                      2 mM  EGTA*       without glycerol                                                                            with 8M glycerol                                1 mM  MgSO.sub.4               and 1 mM GTP*                                   4 M   glycerol                                                                 2 mM  dithioerythritol                                                        ______________________________________                                          pH 6.9 at 23° C.                                                        *MES  2(Nmorpholino) ethane sulphonic acid                                     EGTA  ethylene glycol bis (aminoethyl ether)N,N,N',Ntetraacetic acid           GTP  guanosine triphosphate                                              

All manipulations are performed at 4° C. unless otherwise specified. The horse brain is washed in ice-cold BBG buffer and superficial meninges and blood vessels removed. After weighing, cerebral cortices are chopped, homogenised in 75 ml BBG buffer/100 g brain, centrifuged at 6500 g for 15 min. The volume of the supernatant (Vml) is measured and V/10 ml 10 mM GTP (Li salt) in H₂ O added. The mixture is incubated in sealed centrifuge tubes (30 min, 34° C.) in a shaking water bath to polymerise the tubulin. After polymerisation the tubes are balanced and centrifuged at 100,000 g, (1 h at 27° C.) in a pre-warmed rotor. The high-speed pellet is resuspended in V/4 ml BB buffer and the preparation stirred on ice for 30 min and centrifuged at 100,000 g (1 h at 4° C.) to remove the cold-stable microtubules. An equal volume of BB2G buffer is added to the supernatant which is frozen rapidly in 5 ml samples in plastic weighing dishes floated on a solid CO₂ /ethanol slurry, and stored overnight at -80° C. After ca. 18 hours the frozen samples of tubulin are thawed, 10 mM GTP in H₂ O added to give a final concentration of 1 mM, and the new volume (Wml), is measured. The polymerisation/depolymerisation cycle is repeated exactly as above but substituting W for V give twice-cycled tubulin.

2. Turbidimetric assay of tubulin polymerisation

Apparatus: recording spectrophotometer with a 6-position, thermostatted cuvette holder; full scale deflection=0.2 absorbance units.

In a 1 ml spectrophotometer cuvette are mixed 100 μl 10 mM GTP (Li salt) made up in BB buffer, 10 μl H₂) or DMSO--depending on selected drug solvent, BB buffer and tubulin preparation such that the final increase in A_(350nm) is 0.15 units after 16 mins (approx. 100 μl of tubulin prep. or 2.5 mg protein) in a final volume of 1 ml at 37° C. All reagents are stored on ice.

Polymerisation is initiated by raising the temperature to 37° C. and the increase in A_(350nm) of triplicate samples against a reference cuvette is recorded. The reference sample includes a similar incubation mixture either without tubulin or with the addition of 1 mM Ca²⁺. The increase over initial A_(350nm) 10 min after the completion of lag phase (control polymerisation is 80% complete within this time) is calculated and expressed as a percentage of the control value, for a range of drug concentrations. The drug concentration required to give a 50% change (IC₅₀) in the control value is determined.

Results

                  TABLE 1                                                          ______________________________________                                         Compound of Total tubulin polymerisation                                       Ex. No      IC.sub.50 (μm)                                                  ______________________________________                                         1           0.42                                                               2           0.14                                                               3           0.41                                                               4           0.37                                                               5           0.49                                                               7           0.52                                                               8           0.23                                                               9           0.89                                                               11          4.24                                                               12          1.21                                                               ______________________________________                                    

B) P338D₁ Colony-forming Assay Method

In this assay, cells from an in vitro-adapted line of the mouse lymphoid neoplasm, P388 are first exposed to serially diluted concentrations of test compound over a 24 hour period in culture. Thereafter, the ability of such treated cells to form discrete colonies over a 14 day period after resuspension in a semi-solid drug-free medium is determined.

Initially cells in log growth are plated into individual 25 cm² tissue culture flasks each containing a final volume of 5 mls of Hepes buffered RPMI 1640 culture medium supplemented with 10 percent foetal calf serum, antibiotics and test compound. All compounds are formulated initially at appropriate concentrations in DMSO, 25 microliters of which is then added to each flask. All compounds are evaluated at concentrations ranging serially in four fold decrements from a top concentration some four fold greater than that already known to inhibit the proliferation of these cells by about 80 to 90 percent in the primary proliferative assay.

After 24 hrs exposure to the test compound the cells are counted and a known member of live cells transferred to a 15 ml centrifuge tube to which 4 mls of a 0.25 percent low temperature gelling agarose solution in complete RPMI tissue culture medium is then added. After 13 days incubation at 37° C., 1 ml of 1% p-Iodonitrotetrazolium violet is added to the top of each tube and allowed to permeate through the agarose for a further 24 to 48 hrs. This dye is metabolized by living cells to produce an insoluble red crystalline product which facilitates counting of the colonies. Samples are taken from each tube and the number of colonies containing a minimum of 50 cells is determined. The concentration of compound necessary to inhibit colony formation by 50 percent relative to that of control cells incubated under identical conditions but in the absence of the test compound is determined.

Results

                  TABLE 2                                                          ______________________________________                                         P388 D.sub.1 Colony-forming Assay                                              Compound of                                                                    Example No.    IC.sub.50 (M)                                                   ______________________________________                                         1              1.32 × 10.sup.-8                                          2               5.16 × 10.sup.-10                                        3              2.15 × 10.sup.-9                                          4              5.12 × 10.sup.-9                                          5              1.26 × 10.sup.-8                                          7              6.34 × 10.sup.-9                                          8              2.93 × 10.sup.-9                                          11             4.10 × 10.sup.-8                                          ______________________________________                                    

C. Lymphocytic Leukemia P388/O Test Method

CD2-F₁ mice, of the same sex, weighing within a 3 gram range surrounding 20 g, are used for this test. Control and test animals are injected intraperitoneally with a suspension of 10⁶ viable P388/O tumour cells on day 0. In each test several dose levels which bracket the LD₂₀ for the compound are evaluated; each dose level group contains 6 animals. The test compounds are prepared either in physiologic saline containing 0.05% Tween 8 or distilled water containing 5% dextrose and are administered intraperitoneally on days 1, 5 and 9 relative to tumour implant. Doses are on a mg/kg basis according to individual animal's body weights. The day of death for each animal is recorded and the median day of death identified for each group. The difference between the median survival time for treated and control groups is expressed as a percentage increase in life span (% ILS).

Results

                  TABLE 3                                                          ______________________________________                                         Lymphocytic Leukaemia P388/0 Test                                              Compound of                  30 Day 60 Day                                     Example No.                                                                             Dose(mg/kg)                                                                               % ILS    survivors                                                                             survivors                                  ______________________________________                                         1        10         300      6/6    2/6                                        2        7.3         31                                                        3        50         136                                                        4        20          44                                                        5        150         61                                                        7        5          111                                                        8        10          44                                                        9        200        180                                                        11       675        155      1/6    0/6                                        12       675        170                                                        26       300        263                                                        32       750        280             1/6                                        33       200        240             3/6 (Day 51)                               ______________________________________                                    

D LD₂₀ (Mouse) Method

Test compounds are prepared as described for the lymphocytic leukemia P388/O test (C) and administered intraperitoneally at various dose levels to groups of 6 CD2-F₁ mice, of the same sex, weighing 20±3 g, on days 1, 5 and 9. The mice are observed for up to 14 days (from day 1), the number of deaths in each group recorded and the LD₂₀ determined.

Results

                  TABLE 4                                                          ______________________________________                                         Compound of                                                                    Example No.    ID.sub.20 (mg/kg)                                               ______________________________________                                         1              20-30                                                           2               5                                                              3              200                                                             4               20                                                             5              140                                                             7               15                                                             8               15                                                             9              450                                                             11             >450                                                            12             >450                                                            26             450                                                             31             165                                                             32             >450                                                            ______________________________________                                    

E. Activity against drug-resistant tumours

Using a similar procedure to the Lymphocytic Leukaemia P388/O test, the compound of Example 1 was evaluated against P388/O tumours which had been made resistant to the following standard, clinically used anti-tumour agents:

bis-chloronitrosourea (BCNU)

cyclophosphamide (CPA)

adriamycin (ADR)

actinomycin D (ActD)

methotrexate (MTX)

5-fluorouracil (5FU)

Cis-platinum (Cis-Pt)

Vincristine (VCR)

Amsacrine (AMSA)

Results

                  TABLE 5                                                          ______________________________________                                         In vivo activity of the Compound of Example 1                                  against drug resistant tumors                                                  Tumor/             Optimum           60 Day                                    Resistance                                                                              Compound  Dose (mg/kg)                                                                               % ILS Survivors                                 ______________________________________                                         P388/BCNU                                                                               Ex.1      7.5         +131  0/6                                                BCNU      2.0         +36   0/6                                       P388/Cis-Pt                                                                             Ex.1      10.0        +50   1/6                                                Cis-Pt    5.3         +21   0/6                                       P388/AMSA                                                                               Ex. 1     5.0         +134  4/6                                                                            (day 31)                                  P388/ADR Ex.1      10.0        +90   0/6                                                ADR       4.5         +27   0/6                                       P388/MTX Ex.1      7.5         +100  1/6                                                MTX       3.0         +15   0/6                                       P388/ActD                                                                               Ex.1      12.5        +109  1/6                                                ActD      0.5         +27   0/6                                       P388/CPA Ex.1      12.5        +150  1/6                                                CPA       265.0       +55   0/6                                       P388/VCR Ex.1      12.5        +145  3/6                                                VGR       1.5         +36   0/6                                       P388/5FU Ex.1      10.0        +92   0/6                                                5FU       20.0        +71   0/6                                       ______________________________________                                    

F. In Vito Activity Against Human Tumour Cell Lines Method

Cells from the human tumour cell lines DLD-1, HCT-116, WiDr and A549 are exposed to serially diluted concentrations of test compounds over a 96 hour period in culture. The ability of such cells to proliferate over the test period is determined.

Cells in log growth are plated into 96 well multiwell tissue culture dished in 100 μl/well of RPMI 1640 culture medium supplemented with 10% foetal calf serum, antibiotics and test compound. All compounds are formulated initially at appropriate concentrations in DMSO, the final concentrations in this solvent being twenty times that required in the plate. A final 1 in 10 dilution in complete medium is then made before adding 100 μl to each well of the plate. All compounds are evaluated at concentrations ranging serially in four fold decrements from a top concentration some four fold greater than that already known to inhibit the proliferation of cells from the mouse lymphoid neoplasm, P388D1 by about 80 to 90 percent in a primary proliferative assay.

After 96 hours the proliferation of cells exposed to test compound is compared with control untreated cells by one of two methods:

a) Culture supernatants are aspirated and cells fixed and stained by adding a solution of methylene blue (5 g per liter of 50% ethanol:water, 100 μl/well). After 30 minutes at room temperature unbound are solubilised overnight using 1% Sarkosyl (Sigma) in phosphate-buffered saline (100 μl/well). Absorbances are read by an ELISA plate spectrophotometer at a wavelength of 620 nm. The IC50 is defined as that concentration of drug which decreases absorbance to 50% of that in control (drug-free) cultures. This method is used for the DLD-1 cell line.

b) 20 μl of MTT (5 mg/ml in PBS) is added to each well. After an incubation period of 4 hours the medium from each well is aspirated and replaced with 200 μl DMSO to dissolve the formazan crystals formed. Absorbances are read by an ELISA plate spectrophotometer at a wavelength of 540 nm. The IC50 is defined as that concentration of drug which decreases absorbance to 50% of that in control (drug-free) cultures. This method is used for the WiDr, HCT-116 and A549 cell lines.

                  TABLE 6                                                          ______________________________________                                         In Vitro Activity against human tumor cell lines                               Compound of                IC.sub.50 (μM) × 10.sup.-3                 Example No                                                                              DLD-1.sup.(a)                                                                           WiDR.sup.(b)                                                                            HCT-116.sup.(b)                                                                            A549.sup.(b)                            ______________________________________                                         1        11.60    30.00    9.20        23.97                                   2        2.90     4.57     2.80        3.42                                    3        1.35     0.92     1.91        1.92                                    4        6.63     10.98    5.45        20.81                                   5        7.34     3.65     3.30        4.36                                    7        5.92     19.70    8.25        22.40                                   8        8.82     41.00    20.52       38.96                                   ______________________________________                                    

G. In vivo activity of the compound of Example 1 against murine tumours

Using a similar procedure to the Lymphocytic Leukaemia P388/O test the compound of Example 1 was evaluated against the murine tumours B16, L1210 and M5076. A suspension of 10⁶ tumour cells is implanted intraperitoneally into control and test animals on day zero. B16 tumour cells are administered intraperitoneally as a 1:10 Brei of cells on day zero. The test compound is administered intraperitoneally on days 1, 5 and 9. For the B16 and M5076 tests there are 10 mice per treated group and for L1210 there are 6 mice per treated group. The day of death for each animal is recorded and the % ILS (percentage increase in life-span) calculated. The results are given in Table 7.

                  TABLE 7                                                          ______________________________________                                         In Vivo Activity against murine tumors                                                  Dose        Mean % ILS                                                Tumors   (mg/kg)     (± SEM) No of expts                                    ______________________________________                                         M5076    5            28        1                                              L1210    10          134 (±72)                                                                              2                                              B16      5            69 (±4)                                                                               3                                              ______________________________________                                    

FORMULATION EXAMPLES A. Tablet

    ______________________________________                                         Compound of Formula I (as hydrochloride)                                                                100.0 mg                                              Pregelatinised Corn Starch                                                                              60.0 mg                                               Sodium Starch Glycollate 20.0 mg                                               Magnesium Stearate       4.0 mg                                                ______________________________________                                    

The compound of formula (I) is finely ground and intimately mixed with the powdered excipients, pregelatinised corn starch and sodium starch glycollate. The powders are wetted with purified water to form granules. The granules are dried and mixed with the magnesium stearate. The formulation is then compressed into tables weighing approximately 184 mg each.

B. Tablet

    ______________________________________                                         Compound of formula (I)                                                                           100.0 mg                                                    Sodium Starch Glycollate                                                                          20.0 mg                                                     Lactose            83.8 mg                                                     Magnesium Stearate 4.2 mg                                                      Polyvinylpyrrolidone                                                                              14.0 mg                                                     ______________________________________                                    

The compound of formula (I) is finely ground and intimately mixed with the powdered excipients, sodium starch glycollate and lactose. The powders are wetted with a solution of polyvinylpyrrolidone dissolved in purified water and denatured alcohol to form granules. The granules are dried and mixed with the magnesium stearate. The formulation is then compressed into tablets weighing approximately 222 mg each.

C. Capsules

    ______________________________________                                         Compound of formula (I)                                                                           100.0 mg                                                    Corn Starch        50.0 mg                                                     Magnesium Stearate 3.0 mg                                                      ______________________________________                                    

The finely divided compound of formula (I) is mixed with powdered corn starch. The dried powder is mixed with magnesium stearate and filled into hard-shell gelatin capsules.

D. Suspension

    ______________________________________                                         Compound of formula (I)                                                                               100.0    mg                                             Dispersible Cellulose  100.0    mg                                             Glycerin               500.0    mg                                             Sucrose                3,500.0  mg                                             Flavoring Agent        q.s.                                                    Coloring Agent         q.s.                                                    Preserving Agent       0.1%                                                    Purified Water         q.s. to 5.0                                                                             ml                                             ______________________________________                                    

The compound of formula (I) is suspended in the glycerin and a portion of the purified water. The sucrose and preserving agent are dissolved in another portion of hot purified water, and when the colouring agent is added and dissolved, followed by the dispersible cellulose. The two preparations are mixed and cooled before the flavouring agent is added. Purified water is added to final volume. The resulting suspension is thoroughly mixed.

E. IV Injection

    ______________________________________                                         Compound of formula (I)                                                                             5.0 mg                                                    Hydochloric Acid     as needed for                                                                  pH adjustment                                             Water for Injections q.s. to 10 ml                                             ______________________________________                                    

The compound of formula (I) is added to a portion of the Water for Injections. The pH is adjusted with hydrochloric acid to dissolve the compound. Water for Injections is added to final volume and solution is complete after thorough mixing. The solution is sterilised by filtration through a 0.22 micrometer membrane filter and aseptically filled into sterile 10 ml ampoules or vials. 

I claim:
 1. A method of achieving a cytoxic effect against a carcinoma tumour in a host susceptible thereto which comprises administering to said host an effective cytoxic amount of the compound methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo[1,2-b]pyridazin-2-yl]carbamate or a pharmaceutically acceptable salt thereof.
 2. The method of claim 1 in which the carcinoma tumour is colon carcinoma tumour, lung carcinoma tumour or a colon adenocarcinoma tumour. 